The current PR does

• Introduce a PermissionActiveRecord from which models that store permissions should derive from
• Optimizes the indices (primary keys) for the PermissionActiveRecords
  • group_id (and contentcontainer_id/contentcontainer_class) must be first in the index, as those fields are used in all queries, while module_id and permission_id are only used on some queries.
• Enforces types on BasePermission and PermissionManager
• Prepares for transition to use integer group_id also for content container groups and allowing additional group states (e.g. "read-only"/"write-only" or for states: "set-only"/"unset-only"

PR Admin

What kind of change does this PR introduce?

• Code style update
• Refactor

Does this PR introduce a breaking change?

• Yes

If yes, please describe the impact and migration path for existing applications:

Type restrictions as documented in MIGRATE-DEV.md

The PR fulfills these requirements

• It's submitted to the develop branch, not the master branch if no hotfix
• All tests are passing
• New/updated tests are included
• Changelog was modified