Integration with PMD 5.1.
Option pane update, removed language selector since it's no longer necessary, added option to clear error list on save.
merge from master
Use jEdit service API for progress bar widget, better thread handling for updating progress bar.
Bumped version number to 5.0.1 to match PMD version, added dependency on rhino plugin so ecmascript processing works.
Added service for status bar to automatically install the progress bar.
Documentation and javadoc updates.