Rewrite dynamic_ui to store Services data per-session.

Thus set of Services (and cleaned_data for them) for each user/tenant
will be isolated supporting per-tenant isolation blueprint.

Note that SESSION_ENGINE =
'django.contrib.sessions.backends.signed_cookies' doesn't work well
with Services' data storage because it has default limitation of 4096
bytes.

Closes-bug: #1264289
Change-Id: I3d0b46463470912cf6d7a36fddd84292689775da
Merge "Rewrite dynamic_ui to store Services data per-session."