Unregister plugin events on destroy

Switching between plugins handling the same file extension required a
restart before, this fixes it
Only refresh in response to create/delete/rename

Change made to both ProjectTree and SoundPicker. No point refreshing the
list and causing flicker if the only thing that changed is the contents
of a file :-)
Merge branch 'master' of https://github.com/fatcerberus/spherestudio
Fix double-free of events caused by bad merge

Note to self: Don't open pull requests for 2-second fixes unless you're
prepared to deal with merge confusion like this when the pull request
gets closed due to "already did this fix"
Add delay timer for SystemFileWatcher refreshes

When several files in the project folder are changed at once (e.g.,
during a git commit) the file lists were being refreshed over and over
again and locking up the editor for seconds at a time, this adds a
1-second delay after the last watcher event before the list is
auto-refreshed.
Merge pull request #12 from fatcerberus/master

More bugs squashed