datastructures.OrderedDict now has 100% coverage

Fixed some code whose behavior different from stdlib.
Remove unused OrderedDict methods not in stdlib

We should keep OrderedDict's API as similar as possible to the one in
stdlib. This commit removes the "move", "index", "byindex", and
"reverse" methods which aren't in stdlib and aren't used by any code in
Schematics.
Use the same OrderedDict everywhere
Replaced dict.whatever calls with super(OrderedDict, self)
pylint and code cleanup
AssertionError stuff => pytest.raises()
Merge pull request #216 from kstrauser/datastructures-cleanup

Datastructures cleanup