Add C# language support

QBS should support the C# language.

This will be highly relevant once Qt (and QBS) get WinRT / Windows Phone support, since developers will likely want to write portions of their Qt applications in C#.

Things needed:

• C# module
• File tagger for .cs files
• Compiler for .cs files -> .exe/.dll
• Property to specify the language version that should be used (1.0, 1.2, 2.0, 3.0, 4.0, 5.0, see also https://en.wikipedia.org/wiki/C_Sharp_(programming_language)#Versions)

Supporting Mono would be nice, too (this shouldn't be any significant effort beyond the official Microsoft tools). Analogous to supporting MSVC + GCC/MinGW on the C++ side.

According to the documentation on MSDN, "there are no object (.obj) files created as a result of invoking the C# compiler; output files are created directly. As a result of this, the C# compiler does not need a linker."

C# Compiler Options: http://msdn.microsoft.com/en-us/library/2fdbz5xd.aspx