Use language select helper from play-frontend-hmrc

[chrisjameswright]

Use language select helper from play-frontend-hmrc

The hmrcLanguageSelectHelper has been added to reduce the code needed to support Welsh language translation.

Proposed solution

Update views/templates/Layout.scala.html to make use of the new helper. There is an example in the documentation but this will need adjusting to include the toggle and passing through the back link toggle.