Hxl-proxy

- added a new "Logs" tab to show logs from HXL processing
- added UI support for Expand lists filter
- make tagger UI smarter about avoiding duplicates
- remove "whitelist" and "blacklist" throughout code and comments
- fix saved-recipe bug that prevented disabling cloning or removing a description
- added HTML form to set up data-preview API call interactively, and added objects.json format
- ensure that user always returns to select page after login diversion
- added /api/from-spec endpoint to read a full JSON spec (including input and tagger)
- updated to libhxl-python 4.21
- hide unusable data tabs

- fixed bug with JSONPath &selector
- added long description in setup.py for PyPi (from README.md)
- added link files for in-browser tests
- remove unneeded system library from DockerFile

- add UI support for labeling steps in a recipe
- added field on data-source page to specify a JSONpath selector to find the HXL data

- add UI support for new implode filter
- add UI support for flattening JSON lists
- add optional header field for rename-column filter
- add optional &filename= param for /api/data-preview

- added UI support for new Implode filter
- extended Rename column filter to optionally use headers as well as hashtags
- added optional configuration for redis caching (input and output); more needed
- added API endpoint /api/data-preview-sheets to fetch a list of sheet titles from an Excel workbook
- Docker fixes

- minor update: fix HXL_WORKERS check for Docker deployment