Clean up 'plugins/diff/icons/Makefile'
Clean up 'tests/progress_bin*' temporary files
Clean up other left over temporary building files
Rename the method to a more readable name
Remove the big white gap between file diffs
Move navigation panel into history plugin

Resolve #700541
Populate the navigation tree model internally
Notify the navigation when repository changes
Avoid reloading the navigation panel on dash view
Let current view handle reloading when repository changes

This way is really cheap and quick without going throhgh all the user
interface rebuilding process, just let the view handle the reloading
itself, the view should know what is best.
Add a 'on_panel_activated()' method into the panel interface

We have added 'on_view_activated()' method into view interface
previously, so for consistency, we do the same for panel. Let
the panel have a chance to do some work after activated.
Let GitgExtView decide where should GitgExtPanels be placed
Update POTFILES.skip
Port gee from version 1.0 to 0.8