Add Django admin

Issue #43
Add new testing model `School`

Issue #43
Add the school form

Issue #43
Register all models in admin

Issue #43
Sync database

Administration authentication data:
* user name: "admin",
* password: "admin".

Issue #43
Add proper `_has_changed` for HiddenInput

Fixes #45
Merge pull request #46 from mociepka/issues/45

The `_has_changed` in MultipleSelect2HiddenInput return bad data and added admin to testapp.