Changed RigidBodyManipulator.bodies from std::vector<RigidBody> to std::vector<std::unique_ptr<RigidBody>> in preparation for adding a std::unique_ptr<DrakeJoint> member to RigidBody.

Conflicts:
	systems/plants/constructModelmex.cpp
Now creating DrakeJoints in constructModelMex and storing std::unique_ptrs to them in RigidBody objects.

Conflicts:
	systems/plants/constructModelmex.cpp
Now setting DrakeJoint in URDFRigidBodyManipulator as well.

Conflicts:
	systems/plants/constructModelmex.cpp
Cleanup.
Add missing include.
Fixed compile errors on GCC (missing <memory> include and ambiguous call to isinf, see https://bugs.webkit.org/show_bug.cgi?id=59249 for info).
Merge pull request #344 from tkoolen/drakeJointInRigidBodyCherryPick

DrakeJoint in RigidBody