GUACAMOLE-103: Re-merge usability improvements to handling of SAML entity ID property.

The improvements from commit ed7e7bbb84af06433c54f4a58208251ff2772485 were supposed to go to `staging/1.2.0` and then get merged back to `master`, not directly to `master`. The same changes are now being redone against `staging/1.2.0` (to be merged back in again) so that things can be put back in proper sync.