Add docks actions to View menu

[hombit]

Fix #142

Check this GUI features before merge:

• [x] Positive and negative BITPIX images
• [x] Zoom, rotate and flip
• [x] Level control
• [x] Color maps
• [x] Open new image in the same window and in new window

[matwey]

I like it. What do you think about rebasing onto 3.3.x? It seems to be simple enough to be included into stable branch.