(filter) force a reload of filterdns when filter reloads, closes https://github.com/opnsense/core/issues/1396

If we want to be pluggable, simply delete contents of
/usr/local/etc/inc/plugins.inc.d/ and be done with it.

* added dynamic DNS support for Google Domains

* use tabs to be consistent

* add missing error message, last-tested date

(filter) alias range fix, apparently the ranges where unfunctional before refactoring filter_expand_aliases()

(filter) cleanup code, aliasses, globals, etc. loosly related to https://github.com/opnsense/core/issues/1396

(filter) add prio, set-prio to new style FilterRule class as well (plugin support + single parsing in 17.7)