convert to Jekyll based site

[discoform]

Some notes:

I have added or installed the following:

• installed Jekyll
• .gitignore with common Jekyll settings
• added a _data folder for some basic site settings
• added a _includes folder with header and footer template files (removed previous header.html and footer.html files)
• updated links to practicals and other assets
• added a _layouts folder with the base page layout file
• added two CSS files (one for initial Markdown styles, one for custom CSS needs)
• added one javaScript file for the mobile navigation toggle
• add some index.md pages with layout defined and relative includes where needed to ensure content loads
• now includes a 404 error page

I have excluded some files that I don't believe will be needed with the switch away from pandoc, but I can re-add them if necessary:

.travis.yml compile.sh theme.css deploy.sh footer.html header.html