Import export

[jochenklar]

• refactor models to use URI, URI Prefix, and Key
• refactor tests, remove factory_boy
• add test fixtures
• add XML export
• add XML import
• fix i18n switcher
• fix dates in project_answers_tree
• fix yes/no widget

[coveralls]

Coverage decreased (-16.9%) to 62.385% when pulling 18872b3 on import_export into f63c3fa on master.

[coveralls]

Coverage decreased (-16.9%) to 62.385% when pulling 18872b3 on import_export into f63c3fa on master.

[coveralls]

Coverage decreased (-16.9%) to 62.385% when pulling 18872b3 on import_export into f63c3fa on master.

[coveralls]

Coverage decreased (-16.9%) to 62.385% when pulling 18872b3 on import_export into f63c3fa on master.

[coveralls]

Coverage decreased (-16.3%) to 63.017% when pulling e122afa on import_export into f63c3fa on master.

[coveralls]

Coverage decreased (-16.3%) to 63.017% when pulling b530303 on import_export into f63c3fa on master.

[coveralls]

Coverage decreased (-16.3%) to 63.017% when pulling b530303 on import_export into f63c3fa on master.

[coveralls]

Coverage decreased (-16.3%) to 63.017% when pulling b530303 on import_export into f63c3fa on master.

[coveralls]

Coverage decreased (-16.3%) to 63.017% when pulling b530303 on import_export into f63c3fa on master.

[coveralls]

Coverage decreased (-15.9%) to 63.36% when pulling 48c398f on import_export into f63c3fa on master.

[coveralls]

Coverage decreased (-15.9%) to 63.36% when pulling 26ed248 on import_export into f63c3fa on master.