This commit add support for highlighting of indidivual issues,
crosshair support, and changes to mouse based navigation
to make those added features a bit more useful. Here's a
quick summary of what is included in this commit:
-Issue Highlighting
-Edit Pixel Operation Highlighting
-Crosshair Support
-Configurable auto-zoom level support
-Mouse-Based Navigation updates for the issue list, layer preview
and pixel edit mode.
Bryce Yancey
