Add native support of Sonar way to handle multi-module in a .NET solution

In .Net plugins 0.6, multi-module was emulated to show C# projects of a solution as sub-modules.
C# plugins 1.0 will use the new ProjectBuilder extension of Sonar 2.9 to execute an analysis in Sonar multi-module fashion: C# projects of a .NET solution will be executed one after another.
The consequence of this change is that every tool will get executed multiple times (apart from Gallio), which was already the case only for Gendarme in .Net plugins 0.6.