Shields.io style SVG badges 

Hi and thanks for a great plugin! I'm [currently displaying](https://github.com/jan-molak/jenkins-build-monitor-plugin) a Jenkins build badge next to my waffle.io backlog badge and soon the saucelabs badge. I thought that those good old png badges could use a refresh, hence this pull request.

The badge states `jenkins [status]`, so `jenkins passing`, `jenkins failing` etc. so that people can easily distinguish between jenkins and say travis builds should they be displaying their badges next to each other.

This pull request addresses [JENKINS-23062](https://issues.jenkins-ci.org/browse/JENKINS-23062) and [JENKINS-21112](https://issues.jenkins-ci.org/browse/JENKINS-21112).

Best,
Jan