Make DataStore not depend on DbContextConfiguration

This is part of Issue #641 which is about cleaning up the use of DbContextConfiguration. DbContextConfiguration is intended to help resolve dynamic services--that is, services for which the actual type/instance of service to use depends on the current context configuration. However, it has gradually spread throughout the code as a general purpose service locator. This causes dependencies to be hidden and creates a lot of coupling to DbContextConfiguration throughout the code, so I am making a set of changes to help fix this.
You are calling EnsureDatabaseCreated not EnsureCreated, and true is returned the first time and false thereafter. So old name for test seems better? Similarly (just for name) for the non-persistent test below.

Otherwise looks good :shipit: