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.
Use source-agnostic wording for speech role.
Remove special case for DetailedGuide in tests.

Detailed guides have their create button back.
Whitespace.
Change call to action for format advice.
Hint at which subtype is selected in the advice.
Cap the width of the format advice.