Ldap improvements for 4.5

This PR contains all the LDAP changes that are outlined under ticket 8344 (ldap groups) as well as other improvements as time allows. Instructions on reviewing those changes are below. **Some of these changes require a new database version 4.4__1**


 * Fix 1253 LDAP password checks throws exception. Now OMERO refuses to startup if the LDAP connection information is incorrect. This currently is doing a search for all the users and groups, which might be too slow. (~10 sec).



**Note:** I'm pushing this branch now to allow closing tickets, but this branch WILL BE REBASED as soon as gh-283 has been merged.