Put "File upload complete" and "back to folder" together. Turned 'File
upload' into a message, and updated the message styles.
Moved allowed file types into the area where users are uploading files.
This is a temporary fix until js tooltips are implemented, at which
point, these details will be shown when clicking a question mark beside
"Choose files".
Added small animation effect to files when opening iframe to edit. Now
slides down, rather than just appearing open
Linked to silverstripe/silverstripe-cms#223
1. Add arrows to edit dropdowns
2. Adjust lightened fields so they don't look like input boxes, and fix
rgba colours
3. Add ability to click file names to edit
4. Add feedback when edit button is hovered
5. Add feedback if a file has been opened for editing and shut again
(saved changes, unsaved changes, unchanged)
6. Add ability to open and close all files to edit them all at once
7. Add overall feedback for file uploads, and fix NaN error
8. Fix up area to match design
9. Fix error messages so they fit in the provided space
10. Fix case where a single uploaded file errors
