WIP ActuatorStateHandle inherits interfaces from base classes

[bmagyar]

Implementation of #2

Todo list includes:

• Make use of base classes as actual interfaces replacing most (hopefully all) occurences of ActuatorStateHandle in business logic, ideally should be defined / used by RobotHW.
• Base classes should relate to contents of ActuatorData ((likewise for JointData in the future). Flat structs are nice but to extend it maybe needs a templatized version?

@jordan-palacios please add any other items you see fit

[bmagyar]

[bmagyar]

The doxygen tools are very good but we need a more mixed view of what's happening.
In the above I think we could replace the transmissionhandle with a more scope-specific handle. This questions whether ActuatorToJointEffortHandle is needed at all since that conceptually stands for the same at that point

[bmagyar]

Closing in favour of #6