Improvements to Plugin Host

I posted this on GitHub before I saw that you don't accept pull requests there, so here it is:

Changes to FileBasedDocument

- send changed() when file name is updated

Changes to Plug-in Host:

- Add new document command
- Save open/closed state of each type of plug-in windows
- Save position for each type of plug-in window
- Open last used file on program launch
- Add current file name to application title bar
- Add command to bring all plug-in windows to front

Code in dropbox:

Hi Roland - sorry, have been busy but will review these today..

Roland, loving your work this morning ... everytime i hit rebuild on the project my plugin opens right where I had it the last time ... mmmmm :)   I can feel my RSI melting like butter in the sun ;-)