Added support for dynamic mail labels/tags management.

The CSS in the UIxPreferences remains to be done.
GUI changes for mail labels management
Added DAV support for mails labels.
Specify color in which TB can grok it.
Update standard tag colors to match TB and improve tags id generation.
Bump copyright and fix whitespace (tab kill)
Convert color picker to an inline widget

The colors are now limited to the colors offered in Thunderbird.
Use modified utf7 for special folder names
Use raw (utf7) name when checking folder type
Merge branch 'master' of https://github.com/inverse-inc/sogo
update news file
Added SOGoMailAuxiliaryUserAccountsEnabled
Fix for bug #2482
Updated news for the recent bug fix
Fix bug following mail tags management CSS changes
Update to 2.1.1
Update Version to 2.1.1 and update news
Update translations
Update ChangeLog
Merge to 2.1.1