Accelerator fixes on left/right arrow keys

[saulgreenberg]

Two fixes needed -when skipping images, the left/right key press should go to first/last image (ie., to reach the beginning and end) . The current method stops if the decrement/incremetn is < or > the first/last image position, which means it stops before reaching the beginning/end

• We need a way to explain the modifier keys that skip images for rapid navigation. Currently, I have menu items that show the shortcut (e.g., View / view next file -> ) Perhaps we need ones that show the other possibilities ? Not a great solution, but otherwise this is a feature that users will not discover.

[saulgreenberg]

Done. -Documentation about shift and control arrow added to the Help User Control (not a great solution as its easily missed)

• Arrow keys with modifiers now goes to first and last image (see changes in TryShowImageWithoutSliderCallback)