Create _licencing.md

rewording information from  Help/FAQ files: _data_license.md, _software.md and _legal.md
Make the new licencing page work
Add link to licencing page from footer
Remove files that shouldn't be there
Remove legal faq entry
Remove another faq entry
Remove another faq entry that is in the licence page
Merge pull request #678 from openaustralia/licencing

Create _licencing.md