prepare trunk for v3.7

git-svn-id: https://plugins.svn.wordpress.org/leaflet-maps-marker/trunk@805060 b8457f37-d9ea-0310-8a92-e5e31aec5664
change stable tag to 3.7

git-svn-id: https://plugins.svn.wordpress.org/leaflet-maps-marker/trunk@805078 b8457f37-d9ea-0310-8a92-e5e31aec5664