Reorganise component tutorials into new, case-specific, groups

[settermjd]

In the discussion of #18, @froschdesign mentioned that there should be a clean separation of the current tutorials into three separate tutorial groups:

1. Component tutorials
2. Mezzio tutorials
3. MVC tutorials

This is because they're all under the title "Components tutorials", which isn't quite accurate. I agree with him and have opened this issue to help see that that change is made.