Add thumbnails for all example images

The thumbnails are scaled to 50% of the original size. Also provide
an ImageMagick based script to automate the conversion.

Signed-off-by: Wolfgang Mauerer <wolfgang.mauerer@siemens.com>
Allow for magnifying images

When clicking on the image, show a popup with the full-resolution
version. Also use the thumbnails with smaller resolutions, and make
sure that the images are responsive and scale properly.

Include ekko-lightbox from http://ashleydw.github.io/lightbox/,
licensed under Apache-2.0.

Signed-off-by: Wolfgang Mauerer <wolfgang.mauerer@siemens.com>
Add copyright headers

The website is licensed under Apache 2.0.

Signed-off-by: Wolfgang Mauerer <wolfgang.mauerer@siemens.com>