Bug 49279: Style upload button correctly in Opera and Firefox

The file input is a pain to style. So apply the styling to the list
item itself. Make the file input invisible using opacity so it is
still clickable. Set a width and height for the purpose of Firefox so
that entire button is clickable.

Bug: 49279
Change-Id: I0ebcb9a569e7dccaea41e3462885e1f607b1c3ae
Merge "Bug 49279: Style upload button correctly in Opera and Firefox"