Models refactoring

Include the mailbox tree in the Account docType
Changed fixtures apropriately
Controllers refactoring

Repercute models change
Add first Imap function (fetch mailboxes)
Use promises
Misc

Enable Promises longStackTrace in development
Fix Mocha with coffee 1.7
Add dependencies
First test suite

Include Dovecot as a test server IMAP
update tests
fix tests
Quick & dirty client fixes

Need review @jsilvestre
Mistake fixes

https://github.com/cozy/cozy-emails/pull/10/files#r16838152
Remove debug logging
Simpler version of mailbox tree for client
fix two bugs
Merge pull request #10 from aenario/master

Server first steps