Blender Git Loki

Animation Channel Filtering Refactor - Part 3 (Visibility Flag Split)

* This (big) commit is aimed at cleaning up the filtering flags used
by the animation channel filtering code. The list of filtering flags
has been growing a bit "organically" since it's humble origins for use
in the Action Editor some 3 years (IIRC) ago now during a weekend
hackathon. Obviously, some things have ended up tacked on, while
others have been the product of other flag options. Nevertheless, it
was time for a bit of a spring clean!

* Most notably, one area where the system outgrown its original design
for the Action Editor was in terms of the "visibility" filtering flag
it was using. While in the Action Editor the concept of what channels
to include was strictly dictated by whether the channel hierarchy
showed it, in the Graph Editor this is not always the case. In other
words, there was a difference between the data the channels
represented being visible and the channels for that data being visible
in the hierarchy.

Long story short: this lead to bug report [#27076] (and many like it),
where if you selected an F-Curve, then collapsed the Group it was in,
then even after selecting another F-Curve in another Group, the
original F-Curve's properties would still be shown in the Properties
Region. The good news is that this commit fixes this issue right away!

* More good news will follow, as I start checking on the flag usage of
other tools, but I'm committing this first so that we have a stable
reference (of code similar to the old buggy stuff) on which we can
fall back to later to find bugs (should they pop up).

Anyways, back to the trenches!