Add hint for users that have misconfigured SeAT-Groups

* This addresses #7

src/resources/views/seatgroups/edit.blade.php

@@ -101,6 +101,13 @@
 
     <h3>Available for whom</h3>
     <p>Select the corporation to which the SeAT Group is bound.</p>
+    @if($seatgroup->corporation->isEmpty())
+        <div class="alert alert-info alert-dismissible">
+            <button type="button" class="close" data-dismiss="alert" aria-hidden="true">×</button>
+            <h4><i class="icon fa fa-info"></i> SeAT-Group is not working</h4>
+            SeAT-Group needs a corporation to set to work correctly. This will prevent members that have been purged from corporation to still keep their roles.
+        </div>
+    @endif
 
     <div class="panel panel-default">
         <div class="panel-heading">