Number View is defaulted to unsigned instead of signed

[ucrdrk]

Being that the only data type supported by LC3 is a 16-bit twos complement signed integer, it would make sense that the default setting for Number View is signed, rather than unsigned as it is now.

I use this application for the Computer Organization course I teach and I warn students to make this change in the settings, but I have many students who forget and are confused when their code is not showing negative numbers.

The fix is should be quite simple. In src/gui/src/renderer/App.vue change settings.number to signed on line 161 would fix this situation.