Fully functional storage extension with file upload

[rgrp]

Previous work in #877 and #879 + #853 (storage API). In this ticket:

• Improve authorization
• Establish convention for laying out files on disk
• Add documentation
• Fix bugs with #879 (does not currently work -- boto may have changed)

[rgrp]

• Merged ckanext-upload into ckanext-storage
• Got existing API systemin in ckanext-storage fully working (e.g. api section was broken -- maybe due to changed boto ...)
• API now supports GET requests and JSONP where appropriate
• Added auth form to API (could be useful for ajax form stuff going forward)
• Improved UI of upload including having ckan based file links (using redirects)
  • Set uploaded-by field on uploaded files
• Checked on AWS And GS

Also did:

• Improved ofs in various ways including change to standard metadata handling and improved testing (see e.g. ​https://bitbucket.org/okfn/ofs/changeset/36fac29b7775)
• Tracked down ​bug with boto and metadata updating on GS and provided patch.