Drop django-redis, in favour of Django's own Redis backend,
because wagtail-cache no longer suppors django-redis.
Drop hiredis, because we got this error when using it with Django's
own Redis backend:
ImportError: Module "redis.connection" does not define a "HiredisParser" attribute/class
Fix a few errors caused by deprecated things being dropped in Wagtail 5
Update old fa-* icons to ones that work with Wagtail 5 (some were already not working in Wagtail 4)
ImportError: Module "redis.connection" does not define a "HiredisParser" attribute/classfa-*icons to ones that work with Wagtail 5 (some were already not working in Wagtail 4)Fox #352