Rename _application layout partial to _application_shared.
Move core markup of constrained and unconstrained layouts into partials.

To allow for cleaner reuse of the (un)constrained markup in other layouts.
Give the existing layouts more use-oriented names.
Move and rename the styleguide base layout.
Merge branch 'layout-refactor-part-deux'
Mount PensionsCalculator (behind a feature flag)

* introduces bowndler for bower/bundler integration
* references pensions_calculator branch on github until
  pensions_calculator released gem is ready to be mounted
Introduce embedded_tool layout for housing engines.
Add mechanism for pulling in an engine’s js via requirejs.
Move bowndler to development group
Various changes to layout integration with the pensions_calculator engine.
Pull RequireJS config into layout not into application.js
Load require config for engine before its main module
Fix incorrect welsh id in routes.
Add smoke test for the pension calculator.

Note that this currently fails due to lack of welsh translations and dependency.

It is also dependent on a feature flag being on.
Switch to an officially released pensions calculator gem.
Merge branch 'mount_pensions_calculator'
Add Bowndler binstub
Move bowndler into the development, test group

This fixes CI as our test.sh script bundles without the development group.
Solidify cucumber feature toggle detection

Now supports tags used against features and scenario outline
Reload routes before and after toggling a feature