feature: when using LdapUserService one can configure Gitblit to fetch a...

...ll users from ldap that can possibly login. This allows to see newly generated LDAP users instantly in Gitblit. By now an LDAP user had to log in once to appear in GitBlit.

feature: when LDAP user synchronization is enabled, one can configure GitBlit to delete all LDAP users from the backing user service that are no longer existent in LDAP. By now LDAP users that were deleted still appeared in the GitBlit user list.