app/lock: add an dbus interface to handle suspend delay problem

the CL is for giving a way for startdde to find which time
screenlock has been showed.
daemon.power need this to handle screenlock showing delay
problem when suspend.

* lock.Hello method only send a Ready signal.
* screenlock will send a Ready signal when webview is ready to
  work.

Change-Id: Ib59e5fa710279ad7794b6f423e99f77fd74b7b54