Image Location patch extension

Just a proposal, feel free to discard if you don't like it.

I've added second method for specyfing location, either to public (through 'location' key) or anywhere (through 'location_upload_path' and 'location_upload_url').

Using the second method, User can set exact location where image will be uploaded and how it will be displayed.

The first method has been extended as well. It now checks how the user specified the location, and he/she can specify it by:
* path('public').'/somepath/'
* 'public/somepath/'
* 'somepath/'