update license to GPLv3
remove piwik
update MinimalNode for django 1.7
add empty VAMDC_APP and CENTRAL_LOGGER_URL to settings_default.py
add the first implementation of a request to the new central logging service, done by a decorator on the sync view-function. also replace mimetype by content_type for all response objects, due to django 1.7
a few fixes that got lost in the previous merge