sync mailboxes WIP
Revert "sync mailboxes WIP"

This reverts commit f4f0968c09ba956d9bb83314e605d021ccb56155.
change some function styles to make them more readable
save lastsync after full sync of a box
add mailboxes sync
bugfix attachments handling
code clean
tests new functions
Merge remote-tracking branch 'brice/master'
[Refactoring] remove all promises
[Refacto] remove unused utils/model.cofffee
Merge remote-tracking branch 'brice/master' into refacto/no-promise

Conflicts:
	server/controllers/messages.coffee
	server/models/settings.coffee
Remove forgotten logging
[bugfix] next link was broken
[bugfix] next link was broken
[bugfix] error handling in pool
Clean up settings management & test it
Clean up settings management & test it
[bugfix] conversation actions
[bugfix] broke test accounts