There are some cases where overriding the opening.bnr names
isn't desirable, such as when someone has several modded
versions of a game that differ in names but not game IDs.
Prior to this, ConfigMain.cpp was a large (52KB) cpp file that contained all of the UI setting code.
This breaks up the config code into subclasses of wxPanel, which are then just instantiated to add to the settings wxNoteBook. This keeps all the settings categories separated from one another and also cleans up the code in general.