[sugar] taskframe and activity resizing

[Erik Blankinship]

Right now, when toggling the taskframe on/off (F5), activities' edges
are covered up.

Is this the default behavior, or should we write our apps to
dynamically resize to the new available screen real estate?  Will the
taskframe's dis/appearance be animated at some point?

Regardless, what event do we listen for to know when the taskframe's
appearance is toggled?