Merge pull request #102 from xiaohanyu/i18n

Fix wrong directory in babel script.
Fix #42 Added OAuth support with Flask-Oauthlib
Fix error when OAUTH config variable is not provided
clean oauth sessions defore any login/registering
Fix requirements_text needs Oauth lib
Fix Linkedin oauth request
Fix google next parameter
Fiz typo
AjaxModelLoader allow definition of filters
added ThumbWidget, ThumbField and ContentImageWidget
Easy way to add images as main_image or general image in subcontents
Filtering channels on media by default should starts with media/model_name
allow identifier in get_main_image to be a list
Channel get_text() to get channel description formatted
allow uppercase extensions for image uploads
fix unicode
Fix #106, integrate babel to setup.py

This is the first step to improve the i18n/l10n of quokka. It just
integrate some method of pybabel to setup.py, which makes it more
portable.

Documentation: http://babel.pocoo.org/docs/setup/