Remove slimmer and plek
Use the govuk_template gem (dev version)
Pull in the styles from static.

Now that we're no longer using static, and only getting the header/footer styles from the govuk_template gem, we need to pull the rest of the styling into the app.
Fix tests now that they're not using the minimal test template

There is now more than one form on the page, so we need to be more
specific in the tests about which one we're targetting.
Remove related placeholders.

This isn't using slimmer, so these serve no purpose.  Also remove the
Skip to related links as there's nothing to skip to.

Also move repeated stuff into layout.
Use released version of govuk_template gem
Bump govuk_template to 0.0.3

normalize and basic are now included in govuk_template, so remove them
from our stylesheets.
Add comment explaining nested layouts
Fix copy/paste typo in css comments
Merge pull request #5 from alphagov/govuk_templates

Switch from using static/simmer to using the gouk_template gem.