CompoundEditor : Make Timeline sizing more robust
CompoundEditor : Make Timeline sizing more robust

There were two problems here :

- We were applying the timeline size hack only when loading a layout. This meant that the layout behaved differently to when it was freshly authored.
- We were applying the timeline size hack even when the tabs were visible. This resulted in a vertically cropped timeline, and also meant that if other tabs were added later, they too would have a useless size.

We now apply the timeline sizing whenever tab visibility changes, and keep with the standard sizing whenever the tabs are visible, so other tabs may be added.

boberfly/gaffer,appleseedhq/gaffer,hradec/gaffer,andrewkaufman/gaffer,ivanimanishi/gaffer,hradec/gaffer,lucienfostier/gaffer,GafferHQ/gaffer,andrewkaufman/gaffer,andrewkaufman/gaffer,andrewkaufman/gaffer,lucienfostier/gaffer,ivanimanishi/gaffer,ivanimanishi/gaffer,hradec/gaffer,ImageEngine/gaffer,appleseedhq/gaffer,johnhaddon/gaffer,ImageEngine/gaffer,boberfly/gaffer,GafferHQ/gaffer,johnhaddon/gaffer,hradec/gaffer,hradec/gaffer,johnhaddon/gaffer,lucienfostier/gaffer,ImageEngine/gaffer,ivanimanishi/gaffer,andrewkaufman/gaffer,boberfly/gaffer,johnhaddon/gaffer,GafferHQ/gaffer,boberfly/gaffer,GafferHQ/gaffer,GafferHQ/gaffer,lucienfostier/gaffer,appleseedhq/gaffer,appleseedhq/gaffer,johnhaddon/gaffer,ImageEngine/gaffer