Make the CallLogAdapter a static nested class.

This is a precursor to extracting the CallLogAdapter into a separate
class and re-factoring it to dynamically build the list of groups.

That should in term help performance on startup, if we can not construct
the whole grouping on startup.

Bug: 5114769
Change-Id: If684a81d10108e4d72249552cb7ced286ec8cbc6