More efficient Event creation and date typing

Create callback package, expand our callbacks
Create event specific callback so we can create events directly
rather than creating them as DBObjects, and reading using putAll
force certain long values to be dates in mongo
Use some guice magic to make event handler loading cleaner

Didn't get rid of EventHandlerLoader yet, but we no longer inject
an injector.  Taking advantage of Guices MapBinder, we can bind
a map of target to event handler for that target.

I replaced EventHandler.getTarget with an annotation so that we
can read the target type more easily from our guice module
Removed some handlers/curators we won't need or use
Merge pull request #660 from candlepin/ckozak/gutterball-events

More efficient Event creation and date typing

Merged in even though Jenkins bombed! Looks good to me.