Add Policy Manager as plugin

Add Policy Manager as plugin

Policy Manager decides next layout by using occured event and current state
based on the policy table.

And Policy Manager is plugin for Window Manager.
Therefore the OEMs can replace it.

This patch provides Policy Manager I/F as reference implementation
and does not have policy table.
Therefore Policy Manager updates each layers
to draw the applications in normal.full area
in accordance with just like activate/deactivate request.

[APIs of Policy Manager class]
  - int initialize(void)
    Initialize Policy Manger.
      input:  none
      output: 0(success), -1(error)

  - void registerCallback(CallbackTable callback_table)
    Register callback functions.
      input:  the pointers of callback handlers
      output: none

    "CallbackTable" type is as follows:
      typedef struct
      {
          Handler onStateTransitioned;
          Handler onError;
      } CallbackTable;

    "Handler" type is as follows:
      using Handler = std::function<void(json_object *)>;

  - int setInputEventData(json_object *json_in)
    Set input event data for the policy table.
      input:  input event data as json_object
      output: 0(success), -1(error)

  - int executeStateTransition(void)
    Execute state transition by using set input event data.
      input:  none
      output: 0(success), -1(error)

  - void undoState(void)
    Undo state only once per once state transition.
      input:  none
      output: none

[Callbacks of Policy Manager class]
 - void onStateTransitioned(json_object *json_out)
   When state transition succeeds, this callback is called.
   The argument json_out has the state after transition.

 - void onError(json_object *json_out)
   When state transition fails, this callback is called.
   The argument json_out has the error information
   like message, inputed event datas and etc..

Bug-AGL: SPEC-1537

Change-Id: I44b771d4145078bf3ea05e26165bb9c1a03b10c3
Signed-off-by: Yuta Doi <yuta-d@witz-inc.co.jp>