Fixed small bug with RefCount

[wpsimon09]

since refCounts member contains object with type Resource calling: refCount[id]++ was incorrect.

This PR fixes this issue. However it also rises a question if we want to keep ref count within the Resource object or simply use int as a value of the refCounts member variable.

so basically there are two choices either we`ll have:

    std::unordered_map<std::type_index, std::unordered_map<std::string, ResourceData>>  refCounts;

or

    std::unordered_map<std::type_index, std::unordered_map<std::string, int>>  refCounts;

The second approach would work with what was initially in the tutorial. Either way is fine so if you have time please let me know which version is better and I will alter this PR respectively.

Based on the rest of the tutorial it seems that niether of those types are correct and instead it is supposed to be

std::unordered_map<std::string, ResourceData>  refCounts;

Thank you !

[CLAassistant]

All committers have signed the CLA.

[wpsimon09]

The rest of the code in the tutorial is structured with assumption that refTypes is

    std::unordered_map<std::string, ResourceData>  refCounts;

I have altered the tutorial where it mattered to match this assumption.

Furthermore some clarification was needed like for example why one needs ResrouceHandle if one can easily call ResrouceManager::GetResrouce(). This was fixed by using private specifier on those methods.