ICheeseknifeObserver: an activity implementing this interface will be notified about all event handlers being invoked

[csm101]

I added a sample app for it.

In this pull request you will find also some minor changes:

1. I added an .editorconfig file, that forces Visual Studio to use the formatting style intended for your project, regardless of the local settings of the development environment of your contributors
2. I added a new CheeseKnifeException for when someone is trying to inject a method for a non-existent resource id. before this it just crashed with a NullReferenceException
3. I added the name of the method that doesn't match the event handler declaration in the message of the exception that gets rised (otherwise it is quite difficult to find the offending method if your class contains many of them

A note about ICheseknifeObserver.AfterCheeseKnifeEvent: it works perfectly (it gets fired exactly at the end of the execution of the method) when the method is a plain void (not async) method, but if the method is declared as "async void" it gets fired immediately. I managed to get it handled correctly, instead, if the method is declared as "async Task"