Do not depend on simplejson from Python 2.7 onwards

### Motivation:
The project depends on `simplejson` to provide the `OrderedDict` class. The dependency is redundant since Python 2.7, because `OrderedDict` is now part of the [collections](https://docs.python.org/2/library/collections.html#collections.OrderedDict) module.

### Changelog:
* Only import `OrderedDict` from `simplejson` if importing from `collections` fails.
* Only require `simplejson` when the Python version used is older than 2.7.
* Bump project subversion.