Fix file upload

File upload fixes:

Basically - the size property didn't really work.
Secondly, the image returned when inserting was not always the correct size.

Fix
Use inline styles to set the size of elements.
Get the image with a AJAX reqest so we know its the correct size (we only have access to builtin sizes in the JS normally)

Bonus
It seemed to be possible to do the media uploader much more simply
Also supports type - so can restrict to only images or pdfs for example.