Add ENV var support

[dbgarlisch]

Similar to command line args, being able to define and manage and group ENV vars on a per-project basis would be spectacular.

For debugging, I often find myself needing to change env vars at the same time I am changing command line args.

My debugging life would be much simplified and less error prone if I could group them together.

Basically, controlling Arguments, working directory (#98), and environment on a per-project basis would be perfect.