More bugs squashed

Bugs fixed:
* Too many pointless tree refreshes. Now it only refreshes if a file is created/deleted/renamed, if only file contents change nothing happens
* Refreshes were stacking to the point of locking up the editor when several systemwatcher events were raised consecutively (e.g. during a git commit, which creates a lot of new files).  I fixed this by adding a timer and only refreshing after 1 second has passed since the last systemwatcher event.