Adding support for absolute position inputs (GPS/LPS systems)

We've tested this on our ROS Fuerte systems with a few GPS systems and an Optitrack system, seems good. Despite my name (rgariepy) being on this, the primary author/tester is Prasenjit Mukherjee (pmukherj@clearpathrobotics.com)

How do we backport this into the Fuerte/Electric repos?