Refactor role-project relationship to use foreign key instead of string parsing

[mihow]

Summary

The relationship between permission groups ("roles") and projects is currently handled by a specially crafted name (string) of the group. I would prefer we implement a custom Group model and add a project_id field. This will simplify a number of queries and allow us to delete several functions.

Related Issues

#693 #727

Implementation

Here are known functions and classes that will need to be updated:

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