Tighten imapuid message check filter.

There's a potential bug here that just hasn't popped up yet.
Don't ignore soft deletes in IMAP/Gmail mail sync backend.
[SCHEMA] Delete soft-deleted imapuids.
Fix IMAP/Gmail mailsync logging.

Oof, we renamed this logger at some point, since we've expanded to
syncing more than just mail.
Update tags API docs.
Revert breaking changes to tests/imap/test_sendmail.py.
move docs to python module, served via different service
update root path info
Better log message for crispin_client.g_metadata().
Drafts support for create new.

Data model, migration
Store in local data store
Test

Also drafts as pluggable.

- No syncback yet.
- No update, delete, send yet.
- No reply support yet.
Update draft + test, redefined db relation too.
Delete draft + test
Update drafts handles invalid update case + test - v2
Rearchitect draft replies. Again.
Drafts minus sending integration v1

Summary:
Both new drafts + replies locally.
Operations: create, update and delete.
Includes migration, tests.

Does not include:
Sending integration,
docs.

Test Plan: Tests included.

Reviewers: spang

Differential Revision: https://review.inboxapp.com/D149
Send v1 + test.

Does not include:
Send reply.
Send-reply v1 + test
Draft creation syncback.
Drafts API v1.
Drafts code refactor + CR changes.