MBS-5941: if beta redirection is on and the redirect hostname is musicbrainz.org, make the header link include unset_beta
MBS-6058: New schema to model deleted/merged entities separately

This new schema allows us to have real foreign key constraints for active
subscriptions, as the bug in MBS-6058 occurs because HumHumXX is subscribed to
artists that don't exist (but also have apparently not been deleted).

The _deleted tables point to artist_/label_deleted rows, which collect lists of
MBIDs that have been deleted, along with the last known name/comment in order
for us to display the deletion clearly in the subscriptions. This data is
probably interesting to customers too, and has uses for us internally (better
404 pages).
MBS-6058: Rewrite deletion/merge code to use new subscription tables
MBS-6058: Rewrite Data layer to have three separate entities for subscription types

It now uses one entity class for subscriptions against entities that are still
'active' (not deleted), another for entities that have been deleted (tracking
the last known name/comment) and another for entities that have been merged.
MBS-6058: Fix subscription emailing script with the new subscriptions model
MBS-6058: Fix the email generation templates
MBS-6058: Factor out the subscribe-on-create logic into a role
MBS-6020: sort work types in the relationship editor as they are sorted in other forms
MBS-6020: sort using the provided _select_all instead, and partition to make the form work
Merge branch 'beta' into mbs-6020-work-types-collation
Making the whole profile thingy a bit more useful and connected
Move donation stuff to profile
Moving donation stuff to profile (II)
MBS-5487: Store link type in 'Remove Relationship' edits, and allow searching by it.
Format HACKING as markdown.
Rename HACKING to clarify that it is a markdown document.
Document how to run pgtap tests.
Set up pgtap extension in create_test_db.sh.
Move ISRC editing to the Edit recording form
Fixing the test