Capr Issue #99: Potential improvements to Capr

[guuswilmink]

This PR is linked to #99.

Suggested functions:
isStandard.R: Given a path to CSV files with at least fields "sourceCode" and "conceptId", along with a database connection with a CDM and vocabulary schema, return a tibble of non-standard concepts. Allows for export of results for all concepts included (including standard). This function can help in quickly identifying non-standard concepts from tables of concept ids.

isStandardDB.R: Checks whether concepts that exist in a database are standard/non-standard and returns the non-standard concepts. The full table of standard and non-standard concepts can be saved as well. This is probably the most useful out of the 3 isStandard functions.

isStandardCS.R: Similar return as isStandard.R and isStandardDB, but performs the check given a Capr ConceptSet class object rather than CSV files. Does not capture source value (as these are not relevant for concept sets).

countOccurrences.R: Given a vector of concept IDs and a connection to a CDM instance, count the number of occurrences of: 1) persons with concept 'x'; 2) records with concept 'x'; 3) persons with concept 'x' or descendants of 'x'; 4) records with concept 'x' or descendants of 'x'
To demonstrate and further clarify this function I have attached a PDF with example usage. Is this already possible within Capr?

@mdlavallee92 I have incorporated your feedback provided in issue #99; please let me know if this is to your expectations.