Add a new OnScreenReply api to agl-service-homescreen

    Add a new event named OnScreenReply. Applications
    can use this event to reply to the homescreen.
    Also update the documentation for this event.

    [Patch Sets 8,9]
    Update ApplicationGuide.md. For details:
        Use master source build agl-service-homescreen-2017.
        Change agl version to EE.
        Add libhomescreen sample code path.

    [Patch Sets 10]
    Delete tailing space.

BUG-AGL: SPEC-985
Change-Id: Iea0c321731fa62cd94fc08fc5e303c20847fd525
Signed-off-by: zheng_wenlong <wenlong_zheng@nexty-ele.com>