Merge branch '56-design-and-implement-the-security-plugin-API' of dev.sourcefabric.org:superdesk into 56-design-and-implement-the-security-plugin-API

Conflicts:
	plugins/media-archive/superdesk/media_archive/api/meta_info.py
	plugins/media-archive/superdesk/media_archive/impl/meta_info.py
Merge branch '56-design-and-implement-the-security-plugin-API' of dev.sourcefabric.org:superdesk into 56-design-and-implement-the-security-plugin-API