Feature: Nest interface implementations

Added nesting of C# classes under their interfaces based on their file names. Assumes that the class' file name ends with the name of the interface minus the I-prefix.

Examples:
`IFooBar`, `IBar`, `MySpecialFooBar`, `FooBar`, `MyLittleBar` -> nests `MySpecialFooBar` and `FooBar` (that means the I does not have to be replaced by something longer) under `IFooBar`, `MyLittleBar` under `IBar`

No VB support, because nesting does not work properly in VB projects - nested files disappear from Solution Explorer, although they are still part of the project and the code inside them is accessible.

I'm not sure about the position in the order of nesters; I just kind of threw it in somewhere at random.