Add cyberchef container, nginx location, and link in layout.html

Hello again,

This is another pull request, intended to address #229

Here are the Changes I am proposing:

dalton/docker-compose.yml

Added an entry for "cyberchef_current"
- image is based off of ghcr.io/gchq/cyberchef:latest
- the official cyberchef docker image, directly from GCHQ, hosted on github container repository

Added a location directive for both the port 80 and port 443 listener for /cyberchef/
- includes resolve 127.0.0.11; to use docker's internal DNS to resolve the hostname cyberchef_current -- this is very important.
- includes proxy_pass http://cyberchef_current/; to redirect users to the cyberchef instance correctly
- in my testing, none of the proxy_set_header directives were required to interact with cyberchef.

Added a list item and link to /cyberchef that becomes a clickable link on the navigation bar
It was initially proposed to use icon-food for cyberchef. I agree this would look great, however, icon-food is NOT available in dalton/app/static/bootstrap/img/glyphicons-halflings.png. According font-awesome, this icon was added with version 3.0 (https://origin.fontawesome.com/v3/icon/food). I have opted to use icon-book instead (menu? recipe book?), but icon-share might be an option as well.

** Results:

The end-product:

When the Cyberchef button is clicked:

The landing page for cyber chef becomes accessible.