Increasing test coverage
Small DRY in the code
* Added a Form Field which can handle HierarchicalModel
* Added a widget which dynamically creates/deletes Select boxes for new levels of hierarchy
* Added javascript for the widget
* Model has methods neighbours and first_child
* Added views and urls into bitcategory which offers AJAX calls for new categories
* Bug fixes in Model
* More tests
* Added view into testapp in order to provide visual testing of javascript