Enable plugin feedback specifying real arm state.

[ahundt]

From @ahundt on March 25, 2015 1:26

Plugin currently runs the arm as an open loop, reading the state and updating the simulation is temporarily disabled. Debug the issues due to closing the loop, perhaps asking on the v-rep forums, and get the system running in closed loop mode again.

Copied from original issue: ahundt/robone#62

[ahundt]

This functionality was merged in https://github.com/ahundt/grl/commit/1572f881eaf7cc935fc187c104014db901787d81

However, it still needs to be made configurable so that it works in other use cases and doesn't assume that there are two arms.