Adds simple web page to display latest webcam images

It should be easy for us to inspect the latest webcam images during
testing, so I've created this little web page to allow that. It refreshes
the page at regular intervals. This change updates the webcam image
capture script so that it copies the image it captures into the display
folder for inspection.

I've ignored the webcam.jpg file in Git, as this will be continuously
updated.
Updates script to take two pictures rather than copying the first one over

I was concerned that there might be a race between copying the image into
the webcam-display folder and the project-latex app moving the
original image into its data storage folder. By taking two images, this
problem is avoided.
Updates permission on web cam script so it can be executed

This allows the cron job to run it automatically.
Merge branch 'features/webcam-display'

To test this, I ran the script on the Raspberry pi to ensure it did the
right thing. I updated the cron job on the Rasperry pi as instructed in
the script.