Add edge-edge contact constraints.

- Added bilateral line-on-line contact constraint with normal non-penetration and tangential stiction.
- Added unilateral edge-edge contact constraint based on the line-on-line Constraint.
- Modified RigidContact1 adhoc test to include edge-edge test case.
- Added BilateralContactConstraints adhoc test to verify energy conservation for a variety of bilateral constraints that form the basis for the unilateral constraints.
Merge pull request #169 from simbody/addEdgeEdgeContactConstraints

Add edge edge contact constraints