Work on issue #17477510: Time change notifications sent too often

This gets rid of the spam from the battery history, by not creating
an event unless the wall clock time has changed by more than
+/- 500ms.

We'll do the remaining work in MR1.

Change-Id: I8d1cc41b5504261033d3b0ccdcf9e7cf70df9d04
1 file changed