Sit on chair / Get up Behaviours

Added new behaviors for sitting on chair /getting up. Character now has a property telling whether it is seated in some place.
Changed body actions to have an animation for the character to perform when it's standing and another one when it is sitting. Actions themselves where not changed.
Changed move actions so that when the character is seated, it first gets up and then moves.

The syntax for these new behaviors is:

behaviour: sit on a given chair type available in the scenario
name: "sit-on-chair"
parameters:

• "target" - the tag representing the type of chair available in the set where to sit the character (e.g.: "arm-chair", "simple-chair")

action: get up from the chair where the character is seated
name: "get-up"
parameters: none