Add support for different version-streams

[sgallagher]

Oftentimes, different releases of Fedora/EPEL require us to monitor more than one version stream from an upstream project.

For example, the Node.js project: on EPEL 7, I'd like to have Bugzilla tickets automatically opened against new releases in the Node.js 6.x stream, but on Fedora 28 I'd like to have updates about Node.js 8.x and on Fedora Rawhide I might always want the absolute latest one.

It should be possible on release-monitoring.org to specify multiple expressions that should generate Bugzilla tickets.

[QuLogic]

Useful also for Haskell where we (try to) track packages in some LTS setup. @juhp

[Zlopez]

This will be probably satisfied with implementation of #230

[Zlopez]

#230 is already in the-new-hotness, but I need to add new monitoring options to dist-git to make it available for the users.

[Zlopez]

Pull requests for the dist-git were created:
https://pagure.io/pagure-dist-git/pull-request/151
https://pagure.io/pagure/pull-request/5294