RobotHWGroup Implementation

[kphawkins]

I have implemented a RobotHWGroup which seems to match the spec we have been discussing. Currently, it doesn't support multiple identical interfaces across different RobotHW. It returns first the locally registered interface, or then one of the interfaces in one of the RobotHW, ordered by when each was registered.

[jenkins-auto-bot]

@kphawkins Awesome! One comment: to reduce the number of indirections between the derived classes, can you have the RobotHWGroup class completely override the implementation of get, instead of re-using the implemenation of get in RobotHW and have that implementation call through to your subclass. That would result in code that is easier to understand.

[kphawkins]

Unfortunately, that is not possible. Template methods cannot be made virtual so a call toget<T>() inside of ControllerBase would always use the base version. That's why I used this convoluted technique.

[wmeeusse]

@kphawkins That makes sense, thanks for the explanation!

[kphawkins]

Fixed interface aliasing issue: #138

[bmagyar]

This I believe is now safe to close as #231 addressed this feature. Please open a new one if you have suggestions to improve that implementation.