Revert "schema mode: removed unnecessary forced default value #57"

This reverts commit acd1a9bad18c53941e9243f7f2d05f77162c5138.
Revert "simplification of deconstruct method, less is more"

This reverts commit 3df770981a9258f8039d477e8acf58f328906866.
Fixed compatibility with south migrations, #57
Simplified INSTALLED_APPS in test/settings.py
Updated django versions in .travis.yml