F hand driver prefix

Fixes #41 
Yes, I'm printing the params that the driver tries to read:

```
[ INFO] [1412010944.548504021]: Trying to read mapping for: /hand/mapping/1098
[ INFO] [1412010944.551365977]: Trying to read joint_prefix for: /hand/joint_prefix/1098
```

It should be in the launchfile and in the readme.