classic-ui: add support for gzip compressed logs #4519

This commit adds support to read gzip compressed log files
in cgis. It also adds a new cgi.cfg option "read_gzip_logs"
which is disabled by default for now. If read_gzip_logs is
switched on and your compressed log files are still quite
big, it could have a negative impact on the performance of
systems under havy load as every file has to be decompressed.

If you have a small environment, you can switch on
"read_gzip_logs" and compress your logs under archives with
a cronjob every night and save some space.

You can also disable the reading of compressed logs via
configure with "--disable-compressed-logs".

This is my little xmas preset to the icinga community ;-)

refs: #4519
whatthecommit: Well, it's doing something.
classic-ui: fixed add support for gzip compressed logs #4519

well it was late, should work now.

refs: #4519
whatthecommit: Nothing to see here, move along
classic-ui: added config option read_gzip_logs to config.cgi #4519

refs: #4519
Merge branch 'feature/support-compressed-logs-4519' into next

Fixes: #4519
Conflicts:
	Changelog