[sync_states] Add more sync states and handle auth/connection errors more gracefully.

Summary:
[sync_states] Add additional sync states so we can catch exceptions from propagating too far.

[sync_states] Add support for gracefully exiting a mailsync on various errors.

Test Plan:
sync an account that doesn't have proper credentials and ensure that the exception doesn't propagate to email

Fixes T214

Reviewers: spang

Reviewed By: spang

Subscribers: emfree

Maniphest Tasks: T214

Differential Revision: https://review.inboxapp.com/D290

Conflicts:
	inbox/mailsync/backends/imap/imap.py
	inbox/models/account.py
	migrations/versions/071_more_sync_states.py
[sync_states] Add additional sync states so we can catch exceptions from propagating too far.

Conflicts:
	inbox/models/account.py
	migrations/versions/071_more_sync_states.py