improve facet layout, max 8, sort by count, reset

[pvgenuchten]

Overview

This improves some aspects on facets display in items html:

• order by count
• show first 8 buckets and a button to open more buckets
• add a reset button to those facets which are applied as filter
• hide facet if it does not contain buckets
• fix a bug on duplicate filter add in url

v

Related Issue / Discussion

resolves #1066

Additional Information

related to #1065

Contributions and Licensing

(as per https://github.com/geopython/pycsw/blob/master/CONTRIBUTING.rst#contributions-and-licensing)

• I'd like to contribute [feature X|bugfix Y|docs|something else] to pycsw. I confirm that my contributions to pycsw will be compatible with the pycsw license guidelines at the time of contribution.
• I have already previously agreed to the pycsw Contributions and Licensing Guidelines

[tomkralidis]

Alphabetize standard imports:

import logging
from operator import itemgetter
import os
from urllib.parse import urlencode, quote

[pvgenuchten]

Done ✅

[pvgenuchten]

Thanx tom