Uninstall refactor

Uninstall refactor

Split removePiholeFiles into functions for each category.

Reorder execution so that:
  Pihole-FTL is stopped and removed before shutdown scripts are removed.
  User and group are removed before needed commands are removed.

Remove database and log files in user-specified non-default locations,
and use local directories from basic install.sh, falling back to defaults.

Remove use of sudo as the script already checks that it is called as root.

Advise user of location of crontab backup if is created

Make use of service control functions, command detection and default
directories from basic_install.sh

Align variable names with current basic-install.sh

Disable pihole-FTL service immediately, if systemctl is available

Call systemd daemon-reload after removing service files (on systemd systems)

Signed-off-by: Rob Gill <rrobgill@protonmail.com>