Remove dynamic allocations from "impl" layer of motor control interfaces

[valegagge]

In order to fix the issue #1660 , I allocated temporary buffers dinamiccally.

As suggest by @lornat75 , It is better remove dynamic allocations from "impl" layer of yarp despite of performance test results, for two reasons:

• the "impl" layer could be used on embedded in the future
• it is preferable to have dynamic allocations concentrated only at certain points of the code

Therefore I'll develop a simple memory manager to solve this issue; it could be used in other contex also.

see PR https://github.com/robotology/yarp/pull/1668

[drdanz]

If the issue is related to multi-threading, perhaps declaring the buffers thread_local can help? Maybe not, I don't know the details of the issue... :stuck_out_tongue_closed_eyes: