F hand driver prefix

Fixes #41 
I don't know.
I think a prefix is more easily readable by a human than a suffix.
If you are doing rostopic echo this
`rh/EtherCAT Dual CAN Palm`
seems more visible than this
`EtherCAT Dual CAN Palm/rh`

Anyway this is normally used by the aggregator, so, provided that we define the corresponding yaml file conveniently, things look good in the diagnostics GUI plugin.

I've tested them with the yaml in:
https://github.com/shadow-robot/sr-config/blob/F_bimanual_single_loop/sr_ethercat_hand_config/diagnostic_analyzer_bimanual.yaml