Ensure pages don't output empty <h1>s

[sarahmonster]

All pages are currently outputting empty <h1> tags:

Not great for accessibility! It looks like we're passing a bunch of data to the PageHeader component, but the component has been simplified to only show children as a prop.

So instead of:
<PageHeader pageTitle={title} summary={summary} description={description} />
the fix would be to use:
<PageHeader>{title}</PageHeader>

Alternatively, we could refine the PageHeader component to accept more props. This tends to be a common pattern I use for sites, so I'm tempted to opt for the latter approach, although I'm happy to hear dissenting opinions. @tofumatt, thoughts?