UI::update_transport() now calls redraw_playhead() of canvas widgets regardless if transport is running (fixes bug where transport play head not updated when home button clicked and not running).
Bug fixes in Grid::change_update() where height was not being assigned.
Was causing unpredictable issues with Phrase editor and unnecessary complete redraws in Pattern editor.
Added Canvas::Canvas_Panzoomer::damage_grid() for doing partial updates of panzoomer.
Panzoomer damage_grid() now chained from Canvas::damage_grid().