start page improvements

Added a Youtube video describing case study 2 from the paper and
removed the heading for "Something not working?". It was just
redundant and basically only served a purpose during development.
anchors are clearer

The previous styling of anchors made it difficult to see the
links. Now it's been modified with a dotted underline to make this
more obvious. Also, the color was slightly modified as well.
improved styling of documentation page

The styling has been improved so that sections are clearer, and that
should make it easier to read and to find stuff on the page.
fixed png output for motif search

The PNG output for the motif search TOMTOM call was not configured.
Now it should output PNG logos, at least on the production server.