The view for submission history used to grab the timezone from the database (UTC) and
appeded the TIME_ZONE variable after (could be any time zone). Adjusted displayed
timedate to the TIME_ZONE variable. Added unittest checks the localized datetime
object used by submission history for the expected hour difference.
This required the following changes to the DjangoXBlockUserStateClient
semantics:
1) Changes get/get_many to return XBlockUserState tuples, rather
than state dictionaries or (block_key, state) tuples.
2) Raises DoesNotExist if get_history is called on an XBlock that has
had no data saved to it.
3) Returns XBlockUserState tuples as the results of get_history.
