Added getMotions and refactor
Added unit tests for helper functions
Added getMotionDuration
Add play_motion_helpers documentation
Added isAlreadyThere, motionExists and refactor
Refactor variable names in play_motion_helpers_test
Added header installation
Add new methods and refactor

* Add MotionInfo struct
* Add getMotion method
* Refactor from motion_name to motion_id
* getMotionJoints and getMotionPoints implementation moved to getMotion
* Add unit test for getMotion
Cosmetic changes
Merge pull request #7 from v-lopez/new-features

Added methods to obtain motion metadata