ttserver-3 Use objectify for persistence wiring

Squashed commit of the following:

commit a65cc7aeb663da9c59e33876fb488aeefb80bc5a
Author: Chris Kempton <chris.kempton@ithaka.org>
Date:   Fri Nov 1 10:08:44 2013 -0400

    ttserver-3 Increased test coverage

commit 3d2090725e30d05067bad78d20c22480c72b3711
Author: Chris Kempton <chris.kempton@ithaka.org>
Date:   Fri Nov 1 10:08:28 2013 -0400

    ttserver-3 Removed references to DatastoreHelper from all model classes.  Renamed DatastoreHelper as MulticastDatastoreHelper.

commit 9149d00831701d556da678c27ce539675fa1c0ff
Author: Chris Kempton <chris.kempton@ithaka.org>
Date:   Thu Oct 31 16:27:16 2013 -0400

    ttserver-3 Further Objectification remodeling

commit d2d25fe03a7961f10f604a8ff4afb2b0de9353bc
Author: Chris Kempton <chris.kempton@ithaka.org>
Date:   Thu Oct 31 14:44:06 2013 -0400

    ttserver-3 Refactors Device annotation to use Objectify

commit 7885957dc182c8da9f546a7a6e8ba84cbadf2493
Author: Chris Kempton <chris.kempton@ithaka.org>
Date:   Thu Oct 31 13:41:36 2013 -0400

    ttserver-3 Adds test harness for simple Objectify actions

commit c4d99273cb1e5edbea472f9198a85595c1b00b4b
Author: Chris Kempton <chris.kempton@ithaka.org>
Date:   Thu Oct 31 13:40:13 2013 -0400

    ttserver-3 Remodels User and Device classes

commit 9a37b9ecaf07eddeeb8123ea1b53f274479e147e
Author: Chris Kempton <chris.kempton@ithaka.org>
Date:   Thu Oct 31 13:39:09 2013 -0400

    ttserver-3 Registers User class

commit fe5c77432b3d209e395a684b7af34897684b63e8
Author: Chris Kempton <chris.kempton@ithaka.org>
Date:   Thu Oct 31 13:38:26 2013 -0400

    ttserver-3 Adds Objectify filter based on Best Practices documentation

commit 3889820513e38832853b78a9851b6fa301dcb259
Author: Chris Kempton <chris.kempton@ithaka.org>
Date:   Thu Oct 31 13:37:44 2013 -0400

    ttserver-3 Synchronizes deletion

commit e63884b5ad4fde918c985485e9b86da59a6d01ea
Author: Chris Kempton <chris.kempton@ithaka.org>
Date:   Thu Oct 31 13:37:00 2013 -0400

    ttserver-3 Configure appengine dev server for debugging

commit 37aa8d8f439e0a4d40e5fc82c79f850ae85c811d
Author: Chris Kempton <chris.kempton@ithaka.org>
Date:   Wed Oct 30 16:52:13 2013 -0400

    ttserver-3 Use objectify for persistence wiring