TINSEL: Move object creation from constructor to run()

Moved the creation of _midiMusic, _pcmMusic, _sound and _bmv from
the constructor to run(). It was reported on the forum that the
MT-32 emulator didn't work for Discworld, and I'm speculating that
this is because it was being initialized before the "extra path"
had been added to the search path.

It's likely that not all of these objects are needed for every
version of the game. Fixing that is left as an exercise for
someone more familiar with the different game versions than me.