This uses the two-point geometry manager to split the logic of the ruler
geometry and the preview item display. This allows the ruler to use that
manager's angle snap feature.
This allows to measure between features on a PCB. It uses a preview
EDA_ITEM in common, but due to the use of the IDs, it's currently
Pcbnew/Modedit only.
This also adds several "utils" for graphical functons useful when
drawing preview items on GAL canvases.
Fixes: lp:1467313
* https://bugs.launchpad.net/kicad/+bug/1467313