Support source versioning

When introducing an updated version of a CDM into webAPI, prior versions for a given source are lost if you want to use the same source_key. We'd like the ability to be able to retain prior versions of sources to generate analyses against, and choose the source to execute against during cohort/analysis generation.

Proposed solution:
Because many of the WebAPI routs depend on a source_key and adding a version_id would be cumbersome. So, our solution is to add columns to the Source table:

• GROUP_KEY: a varchar field used to group sources together (for example, different versions of the same source would share a group_key)
• GROUP_PRIORITY: Similar to the daimon priority, this is used to indicate the 'preferred' source within a group.
• VERSION_ID: the id of this source
• VERSION_DESC: a varchar form of the source (such as "1.0.0")
• ACTIVE: an int field (0 or 1) used to indicate that the source is not avilable, used to hide it from clients without deleting the record from the DB.

These sources will still be referenced by a unique SOURCE_KEY value in the source table. This is to keep better comparability with existing WebAPI routes.