Added files needed for the Web-Frontend to the image

Signed-off-by: Christian Ege <k4230r6@gmail.com>
Added some packages

- Python PIP for debugging
- MJPG-Streamer for webcam streaming

Signed-off-by: Christian Ege <k4230r6@gmail.com>
Added octoprint user and home directory

The octoprint user is added to the group dialout to get access to the
USB serial attached  printer.

Signed-off-by: Christian Ege <k4230r6@gmail.com>