Frame, dialog and config file couldn't agree on whether to use
internal units or not.
Frame now stores internal units, and they're now mapped on the
way in/out of the config file. Dialog was already assuming they
were stored in internal units (though they were previuosly not).
Fixes: lp:1751435
* https://bugs.launchpad.net/kicad/+bug/1751435
Fixes a bunch of errors:
- libedit and libbrowser would zoom to bounding box but centre on canvas
- libedit, libbrowser and gerbview didn’t take the scroll bars into account
- pcbnew didn’t take scroll bars into account or apply the 10% margin
- appending a board file would re-centre, but not re-zoom
Fixes: lp:1504302
* https://bugs.launchpad.net/kicad/+bug/1504302