Create new-style start page for check-vehicle-tax

Use new style start page and link to the beta vehicle enquiry service
Add the usage requirements to the original service
Swap requirements and instructions
Use style guide for requirements heading
Widen the "you'll need" column
add mobile margin
Change related links title to match browse page
Change service URL for check vehicle tax
Merge pull request #577 from alphagov/check-vehicle-tax-start-page

Check if a vehicle is taxed start page
Only import toolkit buttons mixin once
Merge pull request #581 from alphagov/refactor-buttons-mixins

Only import toolkit buttons mixin once
Remove mustache dependancy

It was needed when there was ajax for the frontend but as that is no
longer used it can be removed.
Use title/URL from publisher for new start pages

We're currently hard-coding these in the templates, but there are some
scenarios where it might be useful to have control of them via publisher
Merge pull request #583 from alphagov/link-new-startpages-to-publisher

Use title/intro/URL from publisher for new start pages
Merge pull request #582 from alphagov/remove-mustache

Remove mustache dependancy
Use mustache for search result rendering

So that we can have the same templates for ajax responses and responses
rendered on the server use the shared mustache gem.

Setup to_hash methods on the presenters to return hashes which can then
be used by mustache to render the template.
Update the JavaScript to work with mustache

Use the new json coming back combined with the mustache template to
render the results when they come back.
Add some tests for the new presenter methods