as one of the NRAO priorities
@jott3077 please help to add descriptions.

req. doc:
https://docs.google.com/document/d/17S6JP5s0_6OZGKLYMrDuY9rV86-TR1Vqgcpra4Ocj78/edit

remaining features:

• add a distance measuring dialog and support pixel position input
• support wcs position input
• support style changes: add option for measuring distance on all three sides
• support style changes: distance units, color, line width