Refactor and reorganize listener multiplexers

-Rename manager -> multiplexer where appropriate
-Split into client/server files/packages to minimize amount of code
going into client and keep complexity server side.
-Make GNSS listeners respect location blacklist.
-Add tests.

Test: presubmits + manual
Change-Id: I368e1c6aab1b9bcc1ff771a050431abc8e9c4c00