Add format advice for main types.
Remove duplicated safety checks for GOVUK JS obj.

We use the asset pipeline so all this gets merged
into a single file (or handful of files as set by
the manifests.

We don't need to check for the existence of
window.GOVUK a dozen times in one file.
Add format advice for subtypes.
Add policy supporting page advice.
Remove deprecated / protected subtypes from lists.

Side effect:
This will force editors / speedtaggers to choose
an alternate subtype if one of these is already
selected, which is something currently covered via
validation.