#7 implementation grabbing between obstacle and character : improvement

Related #7

Modify the grab interaction logic

• add left/rightHandContacted flag in Character which indicates the contact status with an obstacle.
• The contact logic is separate from the button pressed
  1. grab button is pressed -> contact status of each hand is checked
  2. trigger grab interaction on character corresponds to hand's contact-status.

I'm not good at control the character with a motion sensor, so please test grab interaction once on your side.