Unify toolbox into sidebar. (#448)

Most of the Project control and styling panels are unified into the sidebar, except for the toolbox which for some reason is orphaned over on one side of the application window and appears to provide no way to configure its position whatsoever.

Ideally make the toolbox able to be docked in the sidebar along with all the other windows, at the very least let us dock the toolbox where we want and give it an autohide option.