Add provider start/stop and reorganize packages

The main change here is adding start/stop() methods to control location
providers. This gives location providers a more well defined lifecycle,
where previously setRequest() was the only lifecycle available. There
will be some listeners we want to register more permanently than simply
based on the current provider request, so this gives us a place to do
that from.

As a result, AbstractLocationProvider was getting to a point where the
distinction between controller methods (should be invoked by the
provider owner) and internal methods (should be invoked by subclasses of
the location provider) was non-obvious and difficult to understand.
Instead we split out a LocationProviderController interface which
explicitly separates the two types of methods.

In addition, we move a whole bunch of classes into the appropriate
packages.

Test: manual + presubmits
Change-Id: Id140928bc6f545cb6f99fd87f9006f97f7601ac5