Work on MongoDB related stuff has started

Hello

I've started the implementation of MongoDB related stuff.

I created the new project - StackExchange.Profiling.MongoDB - and moved MongoDbStorage class there. I threw away some old code, replaced it with newer one. I then used this storage in Sample.Mvc.Mongo project.

As for sample projects: I put them into newly created solution folder, I think it's good idea because in future we might have more and more sample projects, so it's better to group them in one place.

I removed tons of unneeded code from the sample, what's left is just enough to show that the mongo storage is working. Later on I'm going to complete mongo profiler and put samples for it to the same samples project.

And the last one: I'm using Visual Studio 2013 so it made some unfunctional changes to the solution file and to Sample.Mvc projects. I hope it won't affect anything and everyone can still work with the solution using VS 2012. If it's not the case - let me know and I'll refrain from changes to solution file in the future.