ids.cgi: Rework CGI logic to download a new ruleset

ids.cgi: Rework CGI logic to download a new ruleset

* Drop function to show a notice about snort is working.
* Introduce the log_error function which is responsible for log any
  error messages. Currently it writes it to a tempory file, which will
  be read by the WUI, the message will be displayed and the temporary file
  will be released again.
* Introduce a tiny function to easily perform a reload of the generated
  webpage.

Signed-off-by: Stefan Schantl <stefan.schantl@ipfire.org>