Command Design Overhaul

[starcraftman]

Idea for improvement, create a database of available system commands (including missing, checked by recipe verify()). Then when Command goes to invoke one, instead of using env, pick the most relevant one or fail before executing.

Database would have to support at least two entries per command, most relevant $PATH command and built-in pakit command.

Need to think on it some more after I clear some of the other pressing issues.