Tasks & movements

- "Movement" class isn't used now for "global" moves. There's no need to cumulate "global" moves. Class movement should only be used for small movements induces by some kind of physical effects... To move from a point A to a point B, now use Character::goToGround => one movement at a time

- Task "goTo" implemented
- Task "startActivity" implementation begins
- Task "then" keyword introduced for chaining subtasks, and implemented
- GoToAction not used anymore, to be deleted