Add getComplianceMatrix function to expose odeSolver's compliance matrix.
Implementation of Contact and Localization classes for MassSpringRepresentation.

The Contact class enforces the non-penetration constraint, and the Localization class enables tracking a MassSpring's node in global coordinates.
MassSpringRepresentation dof depends on #nodes
Fix inheritance check

Dynamic cast traverses the type hierarchy to check if a class derives from another class; typeid simply compares the current type.
Fix contact implementation
Implement MassSpringRepresentationContactTest
Implement test for MassSpringRepresentationLocalization
Fix cpplint warnings
Add more documentation
Use size_t instead of unsigned int for 64 bit
Move getComplianceMatrix to base class
Fix spaces
Mark overridden methods virtual
Skip expensive comparison
Use more expressive name
Some comparisons need special variables & methods
Improve documentation
Add tests for MassSpringRepresentationContact

Adds constructor test, constants test, and updates the name for the build MLCP test.
Add MlcpPhysicsProblem helper function for adding new constraints

Updating the MlcpPhysicsProblem is similiar for the rigid body and the mass spring cases,
so we can extract the commonality into a helper function, MlcpPhysicsProblem::updateConstraints.
Factor out setup of BuildMlcpTest in MassSpringRepresentationContactTest

- Create base class for test which has reusable components that aren't being tested, i.e.
the endpoints of the spring, the constraining plane, and the physics representation.
- Create helper function for resetting matrices contained in MlcpPhysicsProblem struct.
- Create helper function for defining which node the constraining plane intersects.
- Replace ASSERT_EQ with more appropriate EXPECT_EQ.