add emacs + vim modelines to the MPL license template

TEMPLATE.SOURCECODE.HEADER

@@ -1,3 +1,4 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
 /*
  * Version: MPL 1.1 / GPLv3+ / LGPLv3+
  *
@@ -27,3 +28,5 @@
  * in which case the provisions of the GPLv3+ or the LGPLv3+ are applicable
  * instead of those above.
  */
+...
+/* vim:set shiftwidth=4 softtabstop=4 expandtab: */