Fix Bing Layer in https

Bing changed their URLs for tiles and the current implementation was not working in https. See blog post for more details: http://social.msdn.microsoft.com/Forums/en-US/618e5f6c-7222-446f-b738-7f57a2e2b592/new-url-templates-for-bing-maps-tiles?forum=bingmapsservices
Merge pull request #104 from stilltorik/patch-1

Fix Bing Layer in https