Add sonar vote configuration

Add configuration in sonar settings page, for configuring which vote sonar should cast for each analysis result; so that alerts could result in -2 or -1, warning in -2, -1 or 0 and green light in 0 or +1.

Also add a dropdown multilist, that allows to restrict which measure alerts are considered for casting a vote in gerrit; so for instance you can still have a red alert for some metric, but that does not impact the vote cast to gerrit. 

Both changes are useful for existing big code bases where quality of coding is slowly improving.

Also, update to sonar plugin api 3.3 (makes it compatible with sonar 3.7.x, tested on 3.7.1), fix some typos around, and add a link to the sonar dashboard for the analyzed project.