Split NotificationEntryManager out of StatusBar.

NotificationEntryManager is responsible for the adding, removing, and
updating of notifications among other things, such as their inflation
and their interaction with other Notification*Manager objects.

Bug: 63874929
Bug: 62602530
Test: runtest systemui
Test: Compile and run
Change-Id: I56f8c524875900112cdf9f6120407b61e201172f