COMMON: Add StackException::add(const StackException &e)
GUI: Remove superfluous exception messages

The exceptions thrown by the decoders already specify the format.
GUI: Fix TPC loading after TXB by rewinding the stream
IMAGES: Throw when no mip maps could be loaded

To "detect" that this image is a TPC and not a TXB...
GUI: Mirror all images for display

Since the texture have their origin in the lower left corner.
IMAGES: Flip SBM; make lower left corner the origin

Because all other textures do that as well.