Blender Git Loki

Some ui reorganization of the physics tab:
* Before the different simulations all had a panel with an "add this" button making the whole tab look really messy. It also rarely makes sense to have more than one or two physics things enabled for a single object, so having all the panels in the tab just added a great deal of visual clutter.
* Now there is a single "enable physics for" panel at the top that allows for enable/disable of any simulation. All actual physics panels are hidden until a simulation is enabled.
* There was no "add" button for force fields before, but I added a toggle between "none" and "force" to unify the ui even further.