[IMAP] Completed mail fetching v1

- implement imap_scheduler to control imap processes flow
- deduplication of same email in multiple mailbox
- mail fetching now only fetch diff
- separate account from mailboxes in couchdb
 (problem with big mailbox tree)
- change in client : paginate mail fetching
Fix DovecotTesting import
fix fixtures
built
fix merge mistakes
fix bug for mail with no attachments & rebased-built
debug 4 joseph
debug 4 joseph
debug /w joseph
Merge pull request #25 from aenario/master

Email fetching