Fix model lookup for page-type

Was looking for model.page-type, which broke image fallbacks on page-per-thing. The actual value was on the parent.
Fix config test

The test failed if you modified your local config, which is stupid. Stubbing out fs.existsSync means the environment_config module never looks at your local config because it believes it to not exist.
Merge pull request #752 from alphagov/bugfix/config-tests

Fix config test
Merge pull request #751 from alphagov/bugfix/image-fallbacks

Fix model lookup for page-type
Move error template into server code

Stop using requirejs plugins to fetch and compile.
Move templates for dashboard and page-per-thing into app/server

These templates are only rendered on the server-side so should live in the appropriate place.

Fix bug in mustache template renderer so that it actually works instead of just guessing at the API and hoping.
Support rendering templates without any data
Remove requirejs from template loading in govuk view
Move prototypes template into server directory

Remove requirejs
Move module template into app/server
Move module templates into app/server directory

Add some view structure around them to DRY out the code
Move last template in app/extensions into app/common

So there's only one place to look.
Change task to copy gov uk template to point to new location

The template moved into the server directory, but the grunt task to do this did not get changed to reflect this
Changed `link` property to `href`

Mustache was recognising `link` as being a function on a string (https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/link) so was calling it, and so had a weird embedding of a `<a href="...">...</a>` into the href property.

Changing to href resolves this.
Lint
Fix services page

The templatePath property had become significant in an earlier refactor of govuk view, so could not be re-used for a different role here.
Move grouped-timeseries visualisation views to client directory
Moved tab views into app/client
Move user-satisfaction views into app/client
Move journey graph visualisation into app/client