add param descr of motorFrictionIdentification
Improve documentation of paramHelp
improvements of wbi and iCub wbi

- improve documentation
- fix some bugs (on simulator)
- add estimate types: motor pos, motor acc, motor torque (currently
implemented to be equal to joint pos, joint acc and joint torque)
motorFrictionIdentification 1st draft

- add parameters and rpc commands
- link parameters  to variables
- read robot status through WBI (tested on simulator only)
Add empty files for recursive linear estimator