In pages specific to a service (e.g. dashboard and sub pages) the title
needs to distinguish which service it applies to. This is mainly to give
context to screen reader users who could be managing multiple services.
Implementing this uses template inheritance:
`page_title` includes `per_page_title` includes `service_page_title`
‘GOV.UK Notify’ is inserted into every page title.
Pages that set `service_page_title` get the service name inserted too.
The mesaure on these pages was too short, making them awkward to read.
Also varies the size of text boxes to make them appropriate to the
expected size of content that they will contain.
