fix: use of items rather than iteritems.
HTMLString python 3 and 2 support.
Python 3 and 2 support.
Merge branch 'feature/python3-support' into develop
[WIP] New schema API. Not fully tested.
remove the old schema code
Add the access to the nested children by their FQN in the schema.
enhanced behavior of the schema containers and associated tests
Add tests for the natural items in a json schema.
respect default values of the json-schema draft 4.
add support for array type item.
Merge branch 'feature/schema-api' into develop

New Schema API
Add helpers for dict to HTML attributes converter.
preventive modifications for the side effects of the code refactoring.
new widget base class + unit tests.
remove old widget tests.
widget schema generation.
Add standard text widgets with the new widget api.
Add the standard select widget based on the new widget api.
remove old bootstrap ui widgets.