Merge experimental_z_estimation

v0.3.0
Changelist:
- Refactoring: Separate pose estimation node into "node" and "class" files
- The new features are not communicating any changes to the rest of t
        system, they only publish calculations on new topics
- roslinted

New Features:
- z estimation:
        -> Implement mathematical formula to calculate vertical displacement
                from horizontal displacement and IMU roll, pitch
        -> Interpolate displacement msgs to match IMU msgs
        -> Interpolate IMu msgs as well (likely unnecessary)
        -> Lowpass filter displacements
        -> Debug: publish z estimations and republish incoming IMU msgs

Future features:
- Implement z estimation as kalman filter object

pandora's old work