Modbus sensor refactoring

[persandstrom]

Description:
The modbus sensor needed some love.

I have:

• Moved the coil support to binary_sensor, since it is a 1-bit value.
• Removed the bits part of the sensor register config, since this can be done more efficient with a template_sensor.
• Removed the register support from the switch since it can be done with template_switch.
• Removed unused functions and unnecessary overrides.
• Moved the slave attribute to each register so that it's easier to communicate with several slaves.
• Changed the registers and coils attributes from a dicts to lists.
• Added a length attribute to the register sensor.
• Changed from unit attribute to the more commonly used unit_of_measurement
• Added voluptuous to all modbus components

I will add voluptuous in the next PR

I have not been able to test the binary_sensor or switch since my unit lacks coils, if anyone has a unit with coils I would appreciate some help!

Related issue (if applicable): fixes #
#3038

Pull request in home-assistant.io with documentation (if applicable): home-assistant/home-assistant.io#
home-assistant/home-assistant.io#933

Example entry for configuration.yaml (if applicable):

modbus:                                                                                                         
  type: serial                                                                                                  
  method: rtu                                                                                                   
  port: /dev/ttyUSB0                                                                                            
  baudrate: 9600                                                                                                
  stopbits: 1                                                                                                   
  bytesize: 8                                                                                                   
  parity: N   

sensor:                                                                                                                        
  - platform: modbus                                                             
    registers:                                                                   
      - name: Fan Speed                                                          
        slave: 1                                                                 
        register: 100                                                            
      - name: Temperature set                                                    
        slave: 1                                                                 
        register: 206                                                            
      - name: Supply air                                                         
        unit_of_measurement: °C                                                  
        slave: 1                                                                 
        register: 213                                                            
        scale: 0.1                                                               
        precision: 1                                                             
      - name: Extract air                                                        
        unit_of_measurement: °C                                                  
        slave: 1                                                                 
        register: 214                                                            
        scale: 0.1                                                               
        precision: 1

binary_sensor:
  - platform: modbus
    coils:
      - name: Alarm 1
        slave: 2
        coil: 15

switch:
  - platform: modbus
    coils:
      - name: Heater
        slave: 1
        coil: 2

Checklist:

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated in home-assistant.io

If code communicates with devices, web services, or a:

• Local tests with tox run successfully. Your PR cannot be merged unless tests pass

[hoopty]

Any chance this can make it into .28?

[pvizeli]

Use BinarySensor instead Entity. See on other binary sensors.

[persandstrom]

The switch is still to be done. Not ready for merge yet

[persandstrom]

The refactoring is done, except for fixes for future review comments.

[fabaff]

For the sake of consistency -> cv.string

[kellerza]

Looks good overall, but I do not have any Modbus kit though. Would be nice if someone can help test it, but as long as the upstream library supports binary_sensor and switch I guess it should be ok

[persandstrom]

I found a modbus slave simulation tool, I can do some simple tests with that.

[persandstrom]

Managed to find a bug from pre-refactoring with the test tool (http://www.modbusdriver.com/diagslave.html). binary_sensor and switch are tested and works

[kellerza]

Looks good! 🐬