2.0.22 Bump
Add support for Django 1.5+

This depends on ModelTree 1.1.5+ for the compatibility fixes.
Update Travis CI config to include Django 1.5 env
Add Haystack search_sites.py module for convenience

Since Haystack requires this file to autodiscover the
search_indexes modules, this is purely for the convenience of
projects which more solely rely on Avocado's search functionality
Remove default search results size of 10

This is arbitrary and has caused confusion that it was truncating
results.
Update CHANGELOG for 2.0.22
Fix bug in parser that limited using primary keys
Update travis-ci config to pre-install numpy and scipy

Add explicit versions to test dependencies
Remove numpy and scipy from `tests_requires`

This is a nuisance with travis-ci since the specified deps are a higher version than what travis-ci provides.
Drop dependency link to jsonfield fork

The latest build in PyPi includes the changes present in the fork
Add language directly to node

This is harmless and more accessible for downstream clients so they do
not have to map the validated node to the corresponding language node.

This is one of the components in migrating to supporting the new
validation implementation. See https://github.com/cbmi/avocado/wiki/Validation
Modify context validation to disable invalid nodes

This takes a more passive approach to validating context nodes, but
prevents the context from getting in an unusable state. Validation
errors result in the node being disabled.
Add `template` and `default` fields to DataContext and DataView

Close #79
Remove unused `DataContext.composite` field
Fix AbstractDataContext __or__ and __and__ hooks

The composite syntax for DataContext nodes were updated in c2329675 to
rely on the `composite` key being present with a primary key. This fix
reflects this new requirement.
Add DataContext and DataView clean method

This checks to ensure only a single default template can be defined at
any one time.
Add support for passing the `json` dict directly into __init__

This is shortcut convenience when working with the API directly.
Change 'in' operator verbose name to sound more natural
Persist enabled flag if false, but allow validation of conditions

This prevents the circumstance when nested nodes are updated without
the language being updated. Nodes will stay-up-date, but will remain
disabled.
Move check for the enabled flag down to the parse function

If attrs are deemed _disabled_, the node itself will not be included in
the context tree. The reason for a node being disabled could be due to
an error which would cause the Node instance to be potentially unstable.
Moving the check to the parse function prevents this issue.