Use of staticfiles to get url to tinymce

This pull request with this one from grappelli https://github.com/stephenmcd/grappelli-safe/pull/25 makes load the tiny_mce in admin and inline editor.

Both are related to #569

I have found other occurrences of STATIC_URL that may break other css and js loading, but did not get to them yet to correct them.I'll make new pull requests when I get to those.