... As when recording starts or stops, or the Tools button has changed, or
scrolling has changed the results of hit-test.
This reduces TrackPanel's intrusions into other code, including ProjectHistory.
Also for AdornedRulerPanel, which shares the base class CellularPanel
... Reimplement the ESC key handling in TrackPanel and time ruler on all
operating systems so that it does not rely on the focused window, but instead
uses the application-wide event filter.
This includes reversion of 9491605cfc
... except Audacity.h; and in no others.
Do so even if Experimental.h gets multiply included, as in both the .h and
.cpp files.
This makes it easier to do a text scan to be sure there are no unintended quiet
changes of meaning because of omission of Experimental.h when the flag is
an enabled one.
Also move inclusions of Experimental.h earlier.
Also don't require Experimental.h to be preceded by Audacity.h to define
EXPERIMENTAL_MIDI_OUT correctly.
