Improve colored Find Usages

I really like the new coloring in Find Usages, thanks for that!

(The only thing I changed was the color for read-access, I think green is better than orange here).

I works really great for POD types, however I think it can be improved for class types (i.e. types with member functions).

Member functions marked const can only do read access, so they should be marked as such.

For non-const functions that is not completely clear, they could modify the object, but must not. Maybe keeping the default color here is Ok.

But I think declarations that already assign a value should be write accesses.