Add new functions for managing process group

Add new functions for managing process group

To manage oom score of child processes of the application properly,
AMD and resourced must know the process ID. When the child process calls
the aul_proc_group_add() function, AMD sends the app group signal to
resourced to notify the process group information.
If the oom score of the main process is changed, the oom score of the
child process is also changed by resourced.

Adds:
 - aul_proc_group_add()
 - aul_proc_group_remove()

Change-Id: Ic02f958bf32110e794efbdacc64c6cf8e3d8cfe4
Signed-off-by: Hwankyu Jhun <h.jhun@samsung.com>