Repository families

(Probably only for D7)

Problem/Motivation

Currently, if two repositories have shared commits, there is no way to relate their entities.
That impacts on the number of rows in the entity tables needed per repository.
A simple example is drupal core. If initiative X push new code on top of drupal core to a new repository, we add all the information about drupal core again to the entities tables, which is lots of rows.

If we have relations between repositories, we can manage more efficiently the entities information on the database.

Please notice that this issue is different to #1546660: Project families, but it could be argued they are related.

Proposed resolution

Create a {versioncontrol_repository_families} table with an ID(and maybe a name, but probably not necessary).
Use that ID on the entities tables to prevent duplicated data.
We only need one ID(opposed to a relation with metadata), because we do not really care about hierarchy.

Remaining tasks

Done. Make the schema changes.
Make entities CRUD aware of the new schema.
Fix manual queries which use information which changed.
Fix views integration to use the new schema.

User interface changes

None.

API changes

Hopefully, none.