ENH: add formatting for ruler distance

Add the Slicer 3 options to select some default formats for how
the distance is shown on the ruler. Uses the Annotations module ruler default.

Adds the distance measurement format to the ruler display node, tests it.
Adds some default format settings in a combo box and a free form line
edit widget to show/set the format in the GUI.

Issue #3367
BUG: use proper button role to remember user preference

The yes button doesn't have a compatible button role to remember
the user preference for the next time the convert all message
box may be triggered. Add a custom button with the accept role
to save the preference.

Issue #3663 and issue #3367
ENH: add label position, tick options

Add MRML and GUI support for ruler label position, max
number of ticks, tick spacing on the ruler widget.

Issue #3367