their handlers based on notifiers, which is simpler and more
reliable.
This fixes for example editmode or uv edit keymaps not working
when creating a new 3dview or image space.
Now the mute/protect/expand/etc. toggles are drawn using UI widgets. This means that special event handling code to determine when they were clicked on is no longer needed, and also means that there can now be tooltips for these items too.
Also, added visibility toggles for ID-block expanders, which will cause all the F-Curves in the linked datablock to not get drawn. The backend filtering code to make this work will come later...
Finally started refactoring the drawing code for animation editors so that all the drawing (of the channels/names list) is done using standardised code for all the editors.
A little specialised system for this has been made, and is now used for DopeSheet and Graph Editor drawing. This should make it easier to add new channel types with less effort.
Protect/mute toggles are now always clamped to the right-hand edge of the channels list. So you can now make the list wider to view longer names fully. However, since the mouse-handling hasn't been fixed yet, this won't always work.
TODOs:
* make mouse-click handling code use this system too, simplifying things to 1-2 lines of code there. Maybe this could be made to use UI widgets instead at a later date?
* NLA still needs to be ported to this system
