Added feature to optionally check switch exhaustiveness when using enums

[Uriel6575]

I've implemented this feature while refactoring some stuff just for myself but thought that it might be useful for somebody else. The main idea here is that C# compiler by default doesn't check that all enum values was used in some switch statement. And it's quite understandable, because sometimes I do really want to handle just 2 of 10 flags, for example. But sometimes I want to be sure that all possible enum values was handled. So here I have an action which adds marker comment to switch statement and then it becomes subjected to the aforementioned check. And also you can add all the missing cases with the fix action.