Restructure tests into views/models/commands subdirectories to mirror the new
source tree structure introduced with ac731bf4 (Restructure source tree).

Deprecates old case-sensitive format. Some software out there stores email
addresses converted to lower case, breaking v1 remailer addresses. The new
format is case-insensitive and generally more robust.

Uffd continues to use and support the v1 format for services setup before
this change. Support for the old format is planned to be remove in uffd v3.
It is possbile to gradually migrate services to the new format with a service
setting in the admin interface.

Also fixes compatability issue with very recent SQLAlchemy versions introduced
by b391e176 (whens parameter of case function).

Preperation for future features that require per-service user settings
or state, e.g. stateful sync or service-specific email settings.

The additional JOIN of ServiceUser degrades getusers API performance
by 30-50%. For API calls that return many users, this is compensated by
an otherwise unrelated optimization (selectinload instead of joinedload).