fix the missing parameters in the play processor

propositional_header and header_class were both missing from the top_of_page
declaration. This was stopping the template from version 0.7.1 to 0.7.2 from
compiling.

I've also renamed their contents to fit scala naming conventions and defaulted
them to `Html.empty` to make it easier for people to upgrade.

I'd like to rewrite the play processor to generate the top_of_page declaration
based on the other items but I don't really know enough ruby to know where to
start.

Also there should be tests here but I don't know enough ruby to know how to
test to ensure any yeilds that do return a value are listed in the top_of_page,
to prevent this happening again.
adding missing htmlLang to the top_of_page and including all defined in yeild in the content_for?
Merge pull request #76 from alphagov/fixPlayMissingParameters

Fix the missing parameters in the play processor
Add underline hover state for main proposition link
Merge pull request #85 from alphagov/add-proposition-link-hover-state

Add underline hover state for main proposition link
Adding updated touch icon sizes
New iOS 7 compatible sizes
Update apple touch icon sizes

Apple have updated the optimal sizes to serve precomposed icons as.
Update the references to the new icon sizes and delete the old ones.

The new sizes and documentation can be seen here:

https://developer.apple.com/library/ios/documentation/AppleApplications/Reference/SafariWebContent/ConfiguringWebApplications/ConfiguringWebApplications.html
https://developer.apple.com/library/ios/documentation/UserExperience/Conceptual/MobileHIG/IconMatrix.html#//apple_ref/doc/uid/TP40006556-CH27
Merge pull request #86 from alphagov/updated-touch-icons

Adding updated touch icon sizes
Fix invalid asterisk selector hack

We already have logical constructs for targeting specific versions of
IE, so we can use those for IE7 instead of the asterisk hack.
Merge pull request #89 from alphagov/fix-asterisk-hack

Fix invalid asterisk selector hack
Bump govuk_frontend_toolkit to latest version

The only change which this effects is gets a new visited link colour.
Merge pull request #91 from alphagov/bump-toolkit

Bump govuk_frontend_toolkit to latest version
Bump to 0.9.0
Merge pull request #92 from alphagov/version-bump

Bump to 0.9.0
Update favicon to include 32x32 image for retina screens
Bump frontend toolkit gem to latest version

Which includes the latest updates for reset the font for print
stylesheets. Which is a font fix for browser and printer issues
reported by users.

https://www.agileplannerapp.com/boards/105200/cards/4633
Merge pull request #94 from alphagov/bump-FED-version

Bump frontend toolkit gem to latest version
Merge pull request #93 from ministryofjustice/retina-favicon

Update favicon to include 32x32 image for retina screens
Bump to 0.9.1 for the font reset to print stylesheets in FED
Merge pull request #95 from alphagov/bump-template-version

Bump to 0.9.1 for the font reset to print stylesheets in FED