AccountSynchronizationMixin was never used on its own and it is a very
confusing class until you understand what it is used for. (It
complemented the Account() class with a few methods to make Account()
syncable.
But we use the SyncableAccount class anyway, so merge the former Mixin'
methods directly in there.
This does away with a class that is not directly used, and was a case of
over-object-orientation which confuses more than it helps.
Touched up code documentation while going through the file.
Signed-off-by: Sebastian Spaeth <Sebastian@SSpaeth.de>
Signed-off-by: Nicolas Sebrecht <nicolas.s-dev@laposte.net>