ENH: adjust ruler display node

Use PointColor1 and 2 for more clarity.
Added line thickness.
Added ruler projection options.
Tests.

Issue #3367
ENH: integrate Markups ruler with Slicer data load/save

Added to the Markups reader class, added more error checking in case
have to try the various storage node readers on ruler or annotation.
Regiter the nodes with the MRML scene.
Removed extraneous warning messages.

Issue #3367
ENH: Convert annotation rulers

Generalised the conversion from annotations to also check
for rulers as well as fiducials.

Issue #3367