change submodule paths to readonly urls

- this change is required so that non-developers can check out the tree without read/write access
- .git/config contains the url that is used for pushing and fetching this can be changed to read/write urls see [0] for more informations

[0] http://365git.tumblr.com/post/12581972612/set-up-a-submodule-where-only-you-have-write-access