Bug fixes and notes for further work for the AUI demo

[halfer]

A few minor fixes for the AUI demo:

• The top gripper switch is now greyed out if the gripper switch is off
• Only closed panes are reopened using the 'Open all panes' button, which prevents currently open panes moving incorrectly in some cases
• Add some comments about investigation into how to redraw panes when their window features (pin, maximise, close) have changed - this still doesn't work in an ideal fashion

I will raise an issue about the last one when I get a moment.

[jgmdev]

Aui stuff is surely a complicated subject, thanks for the hard work 👍

[halfer]

No worries @jgmdev, it's fun! Ping me if you get a chance to look at any of the AUI bugs/crashes later this year, I'll happily do some more demo work.