Merge pull request #10 from mposa/collision-dynamics-integration

Collision dynamics integration
RigidBodyTerrain adds contact and visual geoms.

Right now this is a 1 km x 1 km x 10 m box. Bullet treats infinite planes as
concave objects which messes up our closest distance computations.
Clean up collision filtering in DrakeCollision

I've also enabled collisions between adjacent links in the kinematic tree. We
can take this out if it becomes problematic, but I can think of situations in
which you would want collision detection for adjacent links, so it seems wrong
to disable it entirely.
Remove ground_plane.urdf from fallingSnakeTest
Allow setting terrain to `[]` for no-ground case.
Changed falling snake dt back. Removed ground box from capsules test.
Merge branch 'andres/collision-dynamics-integration'
Add `terrain` option to RBM constructor
Merge branch 'andres/collision-dynamics-integration'
Fixed some unit tests. Changed PlanarRigidBodyManipuluator to pass superclass constructor its options set.