Add support for inline HTML in our T&C modal

The terms widget now uses the "marked" markdown parser library rather than
"markdown-js" as marked supports inline HTML. This is required to create
anchors/links with target="_blank".
Merge pull request #171 from ucamhal/avocet/t-and-c-inline-html

Link to DSpace in T&Cs opens in current page, resulting in form data being lost