upload images, binary files or text files to the repo

Currently, one can click the + New File button to create a new text file, but what if one wants to upload an image to the repo (the actual git repo, not the wiki!)?

We are writing a text collaboratively using rst and Sphinx, but some of the co-authors do not have a git client installed and would like to upload images.

It would also be good to have this option for uploading a source code file (that either doesn't exist in the repo, or replaces the existing version)