Add Orchestra\Auth\Guard::getUserRolesFromEventDispatcher() helper method to clean some code.

Signed-off-by: crynobone <crynobone@gmail.com>
Allow to have null value.

Signed-off-by: crynobone <crynobone@gmail.com>
Merge branch '2.1' into 2.2

Signed-off-by: crynobone <crynobone@gmail.com>

Conflicts:
	src/Auth/Guard.php