This commit simplifies the UI to manage (create, remove, backup,
restore) accounts. It includes the rewording of the previous
Import/Export feature to prevent confusion with the new multidevice
export.
Import is now 'Restore account'
Export is now 'Backup account'
Additionnal label have been added as well

Tuleap: #1152
Change-Id: I64506ce8a2d740f33eeb4719efb4bf8e9f2df746