Add SonarQube coverage support

See #328 
Coverage makes sense when your target is 100%: you want to know if a piece of code you really, really want tested isn't tested. You can set up a piece of your code not to be tested for coverage if it isn't critical.

I personally would find it more useful to know how many lines of code are untested, but given that we receive percentages, I see no reason to have a separate system per language or per team (especially the later, for we hold no information giving it meaning). If we do care about what fraction of critical code is untested, 20% is already too much. If anything, I'd be glad to make it only bright green for 100%, and yellow green between 90% and 95%.