new SolarSystem model-type

Though the only feature implemented is a *very* rudimentary
planet feature so far ...

- new model-type 'solar-system' integrated w/interactive controller
- the planets have a direction and velocity and move
- horizontal and vertical model space wrapping
- view container integrated with layout system
- code and model editors
- model serialization
- tick history
- benchmarks

There's a very heavy pinned planet in the middle.