Fix crash caused by vftable error. Since we are not implementing anything, but only interfacing with the game executable, we need to rename the IConVar variant's due to name ambiguity. Re-defining them in the actual class will lead into vftable misalignment and cause a crash (or other undesired behavior) as a result.
* Refactored ConCommandBase, ConCommand and ConVar class to make them all virtual, so it could interface with the game's implementation.
* Properly initialize members for ConCommand and ConVar instead of just calling memset.
* Fixed bug in ConVar registration function causing the virtual base table pointer to point to the ConCommand implementation instead of the ConVar implementation.
