Update gems
Add more info about thin server errors.
Minor button styling updates. Remove outline.
Add file upload support.

There is definitely an asterisk on this commit because while we now support file
uploads, they are very basic. All image files are automatically uploaded to
mock_file/images as is, and if any two files have the same name one will be
overwritten. It is all very rudimentary, but the ajax uploader works fine.

The other thing is that the uploader does not yet hook into our larger app. It
just does it's job but is largely inaccessible to the rest of the app.
Add image uploading via dropzone.js
Minor tweaks.
Add layer sorting support.
Merge pull request #21 from pxify/iansinnott

File Upload & Layer Support