Release v2.9.1

[v2.9.1]
Divide walk_romeo in two scripts
[cmake] Synchronize
Remove deprecated python scripts.
Restore default walk parameters, changed by error in 6e4283b
Avoid multiple calls to setfeetconstraint.
Allow the waist reference entity to be reachable.
Leave the debian folder to the debian branch.
[Travis] Use submodule.
Correct cmake deps.
Avoid double installation of python scripts.
HerdtOnline does not need arguments.
romeo_walk.py: Correct the name of the robot.