Jekyll conversion

Resolves #1.

Mostly contains Josh's changes as detailed below, with a few tweaks from me. Might want to tidy up the content a little more before merging, but the functionality seems fine. :mag: 

- Ensured all previous pages were compiling correctly with markdown
- Added new directories to contain Documentation, Legacy Versions and Updates
- Added blog functionality i.e. now able to create posts that can be used to describe updates/news regarding APEL
- Added YML files for Site Navigation and Release Versions
- Legacy Versions have been introduced
- Status Markdown from the Repository has also been introduced to the main site