Support watchdog timer

Support watchdog timer

To enable/disable the watchdog timer, appcore uses aul watchdog APIs.
appcore watchdog APIs are added for application developers.

Adds:
 - appcore_watchdog_enable()
 - appcore_watchdog_disable()
 - appcore_watchdog_kick()

Requires:
 - https://review.tizen.org/gerrit/#/c/185276/ [aul-1]
 - https://review.tizen.org/gerrit/#/c/185882/ [app-core]
 - https://review.tizen.org/gerrit/#/c/185884/ [amd]
 - https://review.tizen.org/gerrit/#/c/186247/ [app-common]

Change-Id: I1fc869aed8d54ed473f210eb81d95d25d67a0842
Signed-off-by: Hwankyu Jhun <h.jhun@samsung.com>