URL Handling: Removed referrer-based redirect handling

Swapped back handling to instead be pre-determined instead of being
based upon session/referrer which would cause inconsistent results when
referrer data was not available (redirect to app-loaded images/files).

To support, this adds a mechansism to provide a URL through request
data.

Also cleaned up some imports in code while making changes.
Closes #4656.

app/Access/Controllers/SocialController.php

@@ -91,7 +91,7 @@ class SocialController extends Controller
             return $this->socialRegisterCallback($socialDriver, $socialUser);
         }
 
-        return redirect()->back();
+        return redirect('/');
     }
 
     /**