Remove all references and use of the archive flag in forms

Also, all the tests that tested the archive related code have been removed.
Remove all remaining references to archive(d) flags

This commit also removes all functionality from the *HistoryResource get methods. This will be updated and restored in future versions.
Remove HISTORY_ENABLED related code

This was being read from and undocuemented setting(http://serrano.harvest.io/doc/settings.html) and has no purpose now that the archive argument has been removed from all the post methods.
Merge branch '2.1' into issue-70
Add template for avocado.history.models.Revision model
Add base HistoryResource for getting revisions of a model

This also updates all the *History resources to use to new HistoryResource and includes corresponding tests.
Add tests for the HistoryResource
Remove redundant code from *History resources

Also, remove unnecessary test resource and relocate relevant tests to the ViewHistoryResourceTestCase as the removed resource was essentially the ViewsHistoryResource. The same level of coverage is achieved under these test locations as was previously achieved.
Remove unnecessary import
Add urls and stub enpoints for revision endpoints on objects
Use base uri in HistoryResource and add self links to object data
Remove redundant setUp code by adding new authenticated base class
Add tests for using a custom template in a HistoryResource
Add the embed flag to HistoryResource with relevant tests
Implement ViewRevisionsResource with accompanying test
Rename all *History* methods and references to *Revision*
Implement the ViewRevisionResource with accompanying test

All tests have been updated to conform to the new old_value/new_value
keys being added to fields in Revision.changes by Avocado now.
Remove stub enpoints for retrieving an object as it was at a revision
Move Revision endpoints to base and extend in object resource creation

Previously the revision endpoints were only fully defined for the View
object. The endpoints were significantly abstract that they could be
moved to base under more general names. Now, the object resource files
need only create url patters and create resources for the different
Revision endpoints, supplying the necessary parameters to the Revision
resource in the constructor.
Catch ValueError in ObjectRevisionResource is_not_found()

This should really never happen if urls are constructed correctly but we
can account for the possibility anyway. The ValueErrors from
get_object() are now caught and handled in is_not_found(). Also, tests
have been added to simulate the case where the object id and revision id
are left out.