Call bash -c for all shell commands

An attempt to split all the args and call a process is not how people generally thing to run a "shell command", like the interface for Piper.

Now, instead of calling the command directory, we issue a:

sh -c "command string"

Where the "sh" is actually a call to the user's $SHELL (or "sh" if not set). This should behave as we expect.

This should address Issue #10 (closed)