Better UX for command-line arguments

[alexkreidler]

It is apparent that there has been some confusion (see #104 and #108) about how to pass command line arguments to the program being debugged.

The current solution is to use configuration files. However, should we give command-line args their own spot on the side-panel? For developers of command-line tools, it is important to quickly debug different commands with different arguments. I think this would make it clearer for beginners.