To select a different file with filtron rules, set environment
FILTRON_RULES_TEMPLATE
the default is
utils/templates/etc/filtron/rules.json
The installation is done by the new function install_rules() which offers a
multiple choice in case of collisions (known from searx.sh install setup).
Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>