This fixes the problem on GTK where the text was unreadable when
using a "dark" theme.
And fixes the double display of the real tooltip and the tip panel
being displayed at the same time on GTK and OSX. It seems that
the "disabling/reenabling" of tooltips doesn't take affect right
away anymore...maybe it never did.
It had been causing problems in Unity for a while now and they
were missing on OSX as well in wx3. So, the old menu Open/Close
method of hiding has been removed and replaced with an event
filter/monitor which looks for wxEVT_CHAR_HOOK events to pass
key events to the handler that has the keyboard captured.
It was producing "ghost" windows on OSX in wx3. These were
supposed to be hidden, but they weren't any longer and after
reviewing TipPanel, I realized that there was a separate
code path for OSX entirely...must've gone back to some of the
earliest versions.
Now all platforms use the same bit of code.
