New contact

[tkoolen]

On top of #577. I eventually want to merge this, but it'll take some time. These are all old commits. This will be part of a new major release.

To do (probably an incomplete list):

• ensure that deps that are in our control have RigidBodyDynamics 2 upper bound.
• re-enable all tests
• add compat bounds for new dependencies
• sort using/import statements in Contact.jl
• consistent file names
• Move CoordinateTransformations <-> RigidBodyDynamics type conversions to a better place
• Actually use the GJK stuff (currently just supporting HRep of polyhedral collision geometry, only efficient for low-dimensional polyhedra). Possibly need to add EPA to EnhancedGJK.jl for this
• Actually use CatVector (in ODE integration, to separate contact state from MechanismState).
• Benchmarks: simulating multiple mechanisms.
• benchmarks: contact
• Documentation / update examples