Fix last known bugs in 'annotations fixed to data' mode.

To make an annotation object (eg, label, arrow) be fixed relative to the
data (rather than the plot window) select "Lock Position To Data" in the
dimensions tab of the edit view object dialog.

Behavior:
-the endpoints of Arrow and lines are fixed to the data. Line width and
arrow head size do not scale when zooming

-the center and rotation of label objects is fixed to the data. The
font remains fixed when zooming.

-Boxes: the center, width, and heigh of boxes scale/tranlate with the
data. Rotation stays fixed to the screen. Note: we can't just fix the
corners of rotated boxes to the data, or they wouldn't stay boxes. We
can and do for un-rotated boxes. I'm not totally happy with the
behavior of rotated boxes under zoom.

What is this useful for?
-an arrow and text pointing to an interesting event in the data stays
fixed to the data, even if the plot ranges are changed (eg, the event
scrolls away, or we zoom in.)
-a polygon region drawn in RA/Dec space will stay fixed in RA/Dec
space even if the plot zoom changes.