Issue 336 - LDAP group to teams dont work in 1.3.2

I've implemented a synchronization for LDAP groups. Now it's possible to define a period, in which teams are synchronized with the groups from LDAP.
This makes it possible to see all groups which are available in the configured LDAP-(Subtree) in the gitblit user/group management view. It also removes and creates the teams, when they're created/removed in LDAP (after the configured synchronization period).