Epub fixes

This patch contains various fixes to make epub builds better
1) adds images directory to the epub
2) rasterises all SVGs in the images directory
3) Changes admonition images path so admon images now work!
4) Set images path, so images now also work.
5) Copy common files to the epub
6) set CSS to 'positioning.css'

Partial-Bug: 980305
Change-Id: I04ad09e5144a64bd33fa89891b3bc2f386de9c46
Merge "Epub fixes"