Add ICartesianControl::wait

[PeterBowman]

Fixes #106.

New addition: ICartesianControl::wait command (RPC).

Usage:

• only meant for implementations of movj (relj) and movl, returns immediately otherwise
• blocks until the movement completes or the specified time (in seconds) has elapsed
• 0.0 or a missing timeout value (C++ optional parameter) means no timeout: https://github.com/roboticslab-uc3m/kinematics-dynamics/blob/7ab706f6279fa77f76be5091d41831ee9b31f186/libraries/YarpPlugins/ICartesianControl.h#L271
• returns true or false if errors occurred during the execution of the movement (e.g. maximum joint velocity hit, cannot query current motion status)

Notes:

• not sure about making the timeout parameter optional
• no (safety) check for negative values (but would stop control straight away, see implementation)
• yarp::dev::ICartesianControl::waitMotionDone goes a bit further and introduces the check time period parameter (right now hardcoded to 0.5 seconds)

[coveralls]

Coverage decreased (-0.6%) to 53.488% when pulling 7ab706f6279fa77f76be5091d41831ee9b31f186 on fix-106-wait into 5913c9f4e02ad52ed6f6095a40e929d89adf533f on develop.