resource: display: Add a display monitor thread to deal with multiple clients

resource: display: Add a display monitor thread to deal with multiple clients

When multiple clients request to get fps concurrently,
unacceptable delays (upto tens of seconds for hundred
clients) are incurred. I guess that the dbus function
g_dbus_connection_send_message_with_reply_sync() cannot
deal with multiple concurrent calls.

This patch added a monitor thread to read current fps
value via dbus. The thread shares read fps value to
clients. By doing so, multiple clients can get the fps
value without delays.

Change-Id: I726092658ef79af3610baa6fa356d8a54c6cf299
Signed-off-by: Sung-hun Kim <sfoon.kim@samsung.com>