Refactor block/report dialogs and put into utility class.

+Put all the dialog creation code in one place so they can be re-used
+This is mainly for the after call notification because the same dialogs
will be shown in an invisible activity
+Create listener for determining whether a user checked the spam
checkbox
+Change to DialogFragments for easy reusing of dialogs

Change-Id: I67e13bc0e61952299a4770c9184543ef8b63728a