[Emulator] Add a flag to run a third party app

[Yannis]

Problem you'd like to fix

Debugging a third party app durring its development is pretty difficult because we have to transfer the app each time we want to test it on an actual calculator. Moreover, some bugs in the app could damage the calculator.

Describe the solution you'd like

Add a flag when running the emulator from the command line to load the .nwa app. Add simple debugging where printf() stdout goes to the console.

Describe alternatives you've considered

Add the emulator in the nwlink lib to run the emulator.

[EmilieNumworks]

Totally agreed. It's already planned in our development roadmap. Thanks!