Add data processing how-to-guide

- Updates how-to controllers to set the page title
Move axis customisation how-to guide
Fix axis customisation how-to-guide
Update directive urls

Directives can now work on a server with a path:
`http://webserver/path/to/site/`.
Update axis page title

Also removes Prism and title setting from the how-to item
Fix issues raised in PR
Merge pull request #281 from matthewdunsdon/web/feature/group-processing-how-to

Add data processing how-to-guide