Consider removing NInject dependency

[sharwell]

The NInject dependency seems to duplicate functionality which is normally handled using MEF in the Visual Studio extensibility world. Introducing a different composition mechanism makes it more challenging for users to contribute to the code since the patterns deviate from the more well-known practices.

[rprouse]

Personally I am not a huge fan of MEF, but I am open to the idea if it provides all of the functionality that we get with Ninject. Personally, I find Ninject very easy to work with and think that most developers can come up to speed on it in about 15 minutes so don't think it is a huge barrier to entry.

If MEF is used extensively in Visual Studio however, then Ninject might be redundant.