Support Python 2.6, 2.7, 3.3, Django 1.4+

Currently I've updated project so it supports Python 2.6, 2.7 and 3.3 with Django 1.4+. More variations can be added to tox easily in future. Those would require some updates to importd but wanted those changes to be as small as possible at first.

Tox would run python scripts by itself and ``test_all`` shell script is probably not needed anymore (however I haven't removed it; it can still serve as shortcut to run tests on current environment, not needing to run whole tox).

**Note that I've added two lines to each of single django test apps so they use ``importd`` from repository and not the one installed globally or from ``PYTHONPATH``.**