Bug 30701: Make Upload Tool buttons work on mobile-size screen

Bug 30701: Make Upload Tool buttons work on mobile-size screen

When the Upload tool is accessed on a smaller (mobile) screen (less than
768 pixels wide), the Upload and Browse buttons cannot be clicked. This
patch fixes that.

To test:
1) Go to Tools -> Upload
2) Make the screen narrower, either by opening your browser's Inspector
tool and using Responsive Design Mode, or by dragging in the edge of the
window to make it narrower.
3) Notice that when the screen becomes narrower than 768px, the sections
squash together and the padding between them is lost. Try to click on
the Browse and Upload buttons, notice you cannot.
4) Apply patch and refresh the Upload Tool
5) Ensure the screen is narrower than 768px. Confirm there is now
padding between the sections, and the buttons are clickable again.

Sponsored-by: Chartered Accountants Australia and New Zealand
Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>