Hxl-proxy

- added support for JSON recipes via a &recipe HTTP parameter
- add row queries for clean, count, deduplicate, replace, and
replace-map filters
- use "recipe" and "step" (instead of "filters") on data recipe page
- allow sorting filters/steps
- allow deleting filters/steps
- remove type selector for an already-defined filter/step
- &force=on works for input as well as output
- limit HTML table display to 5,000 rows to avoid timeouts (full
dataset still available via CSV or JSON download)
- add a max_rows parameter to limit the number of rows returned.
- add a /hxl-test page (available in JSON as well)
- modify the append-filter form to add URLs on demand
- support the new multi-URL append filter from libhxl-python

- Add support for requests-cache, so that different views of the same
dataset won't require constant redownloading.
- Add support for a local copy of the p-code GeoJSON shapes tree, for
offline demos (or other purposes).
- Make the list of countries presented in the mapping dropdown menu
configurable.
- Fix exception handling around a missing data source, to avoid
unpredictable behaviour (and incorrect claims of missing HXL hashtags
on first load from Google Drive).
- Start adding scaffolding for jquery-sortable to rearrange filters, but
not supported yet in the backend.
- Remove the sidebar (very slow to download the PNGs in a field
environment).