Add `RigidBodyCapsule` and viewer capsule support

Also adds support for capsule urdf tag.
Switch `collisionDetectGradTest` to use capsules

Also adds `checkDependency('lcmgl')` to that test.
Add capsule test and NOTEST the cylinder test.
Replace cylinders with capsules in `snake.urdf`
Make visual and collision match in `Capsule.urdf`
`fallingCapsulesTest` now uses capsules.
Merge pull request #14 from avalenzu/rigid-body-capsule

Add capsule geometry. This is almost fully supported (works in urdf-parsing, DrakeCollision, BotVisualizer). Still need to implement WRL visualization and planar visualization.