Merge pull request #369 from campusparty/stable/0.2.x

Add manager command to export containerboxes data
Fixes for python 2.6 compatibility
Adds main_image foreign key to channel
Merge pull request #370 from mauler/feature-py26

Fixes for python 2.6 compatibility
Merge pull request #371 from mauler/feature-channel-main_image

Adds main_image foreign key to channel
run test in python 2.6 and 2.7
Fix Channel migration
Removes python 2.6 travis tests
Adds ContainerManager and ContainerQueryset

With these two classes it's possible to call manager methods on
reverse related for example:

{{ channel.container_set.all_published }}
Makes compatible with python 2.6
Fixes pep8 errors
Merge pull request #373 from mauler/feature-py26

Makes compatible with python 2.6
Merge pull request #372 from mauler/feature-container-manager

Adds ContainerManager and ContainerQueryset
Removes unecessary class on inlines

This class it's unecessary for grappelli/opps-admin actually,
but when using with other admin such as django-admin-bootstrapped
or adjngo-wpadmin the inline form is hidden.
Merge pull request #376 from mauler/fix-other-admin-inlines

Removes unecessary class on inlines
Add management command to denormalize channel and containers