[bug] Context loaded from default values of templates via JS should not overwrite system defined variables

[nemesifier]

Testing with 0.8.3 or latest master.
Bug affecting Configuration variables.

How to replicate:

Try defining a template in which the configuration uses {{name}} (the device name).
Add name to the default values of the template.

Assign this template to a device.

Expected outcome:

• context is taken from the default template, but the name key is not added to the device context
• name of device is used in the resulting configuration

Actual outcome:

• context is taken from the default template and the name key is added to the device context, which overwrites the system defined variable
• name defined in the default template value used in the resulting configuration

Best explained with a GIF:

Name should not be added to the configuration variables.

Not just name, any configuration variable from the system defined variables must not be overwritten by the JS which loads the default values from templates.