Modeler extension

[CAS-ual-TY]

This is the second PR that Fabian and me worked on.

I must note: Most of this was uncommited for some time now and when orderly committing everything we realised that there were conflicts now as some new features we added to the modeler were added a couple days ago. The merge was hopefully done properly but review it twice just to be sure.

Emulator additions:

• lwu
• slti
• xor
• srlw
• sraw
• divuw
• remuw

Modeler attitions:

• Reordered these instructions translations to follow the order of instruction.rs and emulator.rs
• Improved addiw to use AND instead of SLL+SRL
• Improved slliw to use AND instead of SLL+SRL
• Improved srliw to use AND instead of SLL+SRL
• Improved sraiw to use AND instead of SLL+SRL
• Improved addw to use AND instead of SLL+SRL
• Improved subw to use AND instead of SLL+SRL
• Add lwu
• Mark slti as unimplemented
• Mark slt as unimplemented
• Mark xor as unimplemented
• Mark rem as unimplemented
• Mark remw as unimplemented
• Mark remuw as unimplemented

I hope there are not too many issues in here. Just let us know and we will fix it. Feel free to squash on merge.