Autosave feature first cut

[adamburkegh]

This pull request primarily adds an autosave feature.

• Periodically, if there are changes in the editor, and it has been X time since the last save, WoPeD will autosave to PNML.
• If the document has not been saved before, it will save to a temporary file in the default WoPeD directories, named autosaveXXX.pnml.
• The autosave period is hardcoded to 30 seconds in DefaultStaticConfiguration.DEFAULT_AUTOSAVE_PERIOD
• I started to change the configuration GUI to make this configurable, but wanted to keep the patch manageable in impact and in effort spent. So this is not in the patch. It would be a reasonable extension.
• There is also some cleanup of dead code and dead TODO comments included.