netcontrol/main.py: Include parent directory in Python path

Since the production code was moved into a different directory, and main.py
was also moved, this stopped working.

This fixup allows developers to do `python netcontrol/main.py` in order to
test their changes in the code, instead of needing to install it in the
system.
netcontrol/main.py: Execute application if it's run from current folder

Developers shouldn't need to install the application in the system in order
to test their changes.

This makes "python main.py" run the application.