[openqa-revtui] Do not hide job groups which have no builds

[b10n1k]

I have a job group in the config file which is not shown up in the openqa-revtui, likely because it has no any build.
It would be nice if there was a way to display info in the output of openqa-revtui instead of ignore it.

[grisu48]

https://progress.opensuse.org/issues/155398 was opened to allow this filtering on the openQA API side and #138 as a solution between.

[r-richardson]

For use with the API there is now also the not_groupid parameter (commit), which accepts 0 for the exclusion of groupless jobs.
You can also filter out groupless jobs in the webui using group_glob=* which is now also shown as a tool tip help message (commit)