Hxl-proxy

- update to libhxl v4.16
- add an admin interface under /admin (need to set a local admin password)
- add an endpoint /api/data-preview to do a raw (no-HXL) preview of tabular data sources
- migrate non-core API calls for P-codes, hash, and hxl_test—to under /api (old URLs still work)
- stay on the recipe page after updating a saved recipe
- fix bug with saving clone permission
- fix bugs with /data/advanced page (for direct JSON entry)
- fix bug in download stub filename (Flask wasn't escaping it)
- major code refactoring with new Recipe class
- remove obsolete iati2hxl endpoint
- improve organisation and documentation for controllers
- added more controller unit tests
- change Dockerfile tag for the base Python image

- fix caching for validation requests sent via POST
- removed obsolete basic chart and map demo

- allow user to provide authorisation token for a private CKAN
dataset or other link that returns 403 Forbidden
- proxy will automatically redirect and start a private dataset
when it detects an authorisation error
- fix 404 error for non-existant P-codes

- fix typo in config file template
- switch to Flask 1.x and Flask-Caching packages
- fix bug in caching for POST validation request
- increase gunicorn max GET request line to 8K characters

- longer cache for P-codes (1 week by default)
- cache results of POST validation service (will fill up cache
quickly with big files)
- bump to libhxl 4.14 for new features and bug fixes

- update to libhxl 4.13.2 for bug fixes and new round() formula
function