HDRI Updates

The old naming convention was "country_city_detail01_detail02".
The new naming convention is "MR_WHR-001_Lighting_Location".
MR allows to easily check if you use one of MR HDRIs and also to filter them by name.
WHR is to define if the HDRI is an EXTerior or an INTerior as it's one of the most important characteristic.
The number is here to easily identify each HDRI.
Then Lighting and Location is the nature of the HDRI.