[VD][Service] Add getApplicationId() for extensions

[VD][Service] Add getApplicationId() for extensions

webapis.getApplicationId() will be used to get the current application
ID by eden preview webapis.
Previously ContentServiceManager is getting the sender application ID
from messsage port parameter, but in case of global wrt-service, it is
org.tizen.chromium-efl.wrt-service, not expected application ID.
So that eden preview webapi can get the intended application ID, this
API will be used in eden preview side.

Change-Id: Ibfeddefe384da92b7ecbeb3d72f14bf5c26c1eef
Signed-off-by: DongHyun Song <dh81.song@samsung.com>