Allow the waist reference entity to be reachable.

It allows for example to change the desired position of the waist
e.g. to crouch, then reuse this entity to restart walking.
Avoid multiple calls to setfeetconstraint.
Restore default walk parameters, changed by error in 6e4283b0be
Remove deprecated python scripts.
Merge pull request #11 from francois-keith/master

Allow to retrieve the waist reference + cleanup of depr files.