Dynamic rate speed/position controller

[joseballester]

Currently the main EGMControl program works at a maximum rate of around 248 Hz (i.e. under 250 Hz). In order to avoid ROSHelper's internal buffer to be filled, the controller node that posts positions or velocities to the command_pose topic should work at that same rate.

As a workaround, the working frequency of the example controllers has been set to 248 Hz manually, but a dynamic choice would be preferable, e.g. reading rostopic hz /sent_pose.