FIX: create an upload when FastImage throws an exception

FastImage might throw an exception when it isn't able to recognize a
file as being an image (ie. happens when users changes the extension
manually)

Also improved upload specs a lot
display the size of the attachment in the preview

instead of adding it during post processing
change the icon in the composer toolbar with a more generic upload icon

also changed all references to "images uploads" to a "uploads"
ooops, fixed CookedPostProcessor specs
Merge pull request #1194 from ZogStriP/uploads

[Upload] Great deal of renaming