construct plane geometry using RigidBodyMeshPoints
parse collision geometry, but is super slow.
support static flag for (much) faster parsing.  fixes some other bugs in sdf parsing.
make more of the terrain block piles static (for efficiency)
replace inspector with draw so I don't get halted trying to solve resolveConstraints.
allow RBMs to load from sdf in the constructor.
allow RBMs w/ no DOF.
uses raycasting to scan the drc terrain, and adds only heightmap terrain to the atlas manipulator.  resolves drc #738 and drc #712.  resolves #634.
commented out second level of angle blocks
Merge pull request #13 from kuindersma/heightmap

commented out second level of angle blocks
Merge pull request #647 from RussTedrake/heightmap

Heightmap