Add configuration setting to control debugger prompt appearance

[daviwil]

This bug is the continuation of bug #130 where we'd like to reduce the noise of prompt output when the debugger stops at breakpoints. For editors like VS Code which have their own dedicated prompt input box, this prompt isn't needed the first time the debugger stops. However, editors like ISE benefit from having the prompt written out so the user knows where to type. In the future we'll need to make prompt output configurable in this case since not all editors need it.