Make sure header logo always links to the root of the main app.
Do not use %W unless interpolation is needed
Merge pull request #624 from moneyadviceservice/header-link-fix

Make sure header logo always links to the root of the main app
Create a class to encapsulate details about a mounted tool.
Move tool routing constraint into ToolMountPoint::PensionsCalculator.

Also now properly enforces locale > tool id conformity.
Implement language translation link.