focus: Added optional focus feature - focus movement by mouse_in.

focus: Added optional focus feature - focus movement by mouse_in.

Focus is moved by mouse click by default. This patch makes moving focus
by mouse_in optionally by configuration and API. Widget item focus
movement is not applied yet. Need to do that as well.

- configuration: "focus_move_policy"
- API: elm_config_focus_move_policy_set/get
- enum
  ELM_FOCUS_MOVE_POLICY_CLICK
  ELM_FOCUS_MOVE_POLICY_IN

@feature