Release Candidate v0.9.1-rc1

• CSCMETAX-61: [ADD] Improve docs. Try to clarify reference data section of datasets.rst. Add examples of ref data use. Add a more detailed example of reasoning how to select reference data for a certain object. Add /_search?pretty=true to ref data table urls.
• CSCMETAX-61: [ADD] Improve docs: Add more stuff about tietomallit.suomi.fi visualizations and its importance
• CSCMETAX-61: [ADD] Improve docs: Changes mostly to make schemas and schema validation errors easier to reason about. 1) Move schema file links from general section to sections where they are more relevant, 2) Add "common schema validation errors" section for hard-to-decipher errors and tips, 3) Change dataset reference data table to contain info when a relation is an array
• CSCMETAX-490: [ADD] IDA and ATT schemas: Make org name non-mandatory. Do mandatory-checking in backend code. To not force end users to provide temporary data that is going to get overwritten anyway, when using identifiers from reference data.
• CSCMETAX-489: [ADD] New HTMLToJSONRenderer, which is enabled in settings.py instead of BrowsableApiRenderer, when debug=False (production). Returns JSON responses, even when text/html is requested in Accept HTTP header, since there is no dedicated html-renderer in use.
• CSCMETAX-491: [ADD] Add script to generate html from swagger.yaml
• CSCMETAX-489: [FIX] Order of renderers in settings.py. ApiErrorView list also appeared to be broken when accept header is text/html (browser accessing browsable api)
• CSCMETAX-61: [ADD] Update app python dependencies, including Django version update