Add a few missing opcodes, fix SRAWI

The missing opcodes are all probably uncommon.

SRAWI was decoding wrong.  I'm not sure how common it is...

Also, update wxWidgets since it was merged.

I've got a separate opcode decoder written and partially hooked up, but not being used yet.  Need to de-virtual the opcode funcs.  The SC change for example is needed since it is more typesafe (and code be even moreso, which I would recommend, e.g. `GPR ra` rather than `u32 ra`.)

-[Unknown]