Header component 'Blog' link is incorrect and ONS logo loses visual focus

### Blog link
Currently concatenates the base url with the item url - but the blog link has a different base url.

Suggest something like (line 333):

`href="{item.url.startsWith('/') ? baseurl : ''}{item.url}"`

### Logo
Logo loses visual focus when accessed via tab key. 

Suggest adding `style="outline: revert;"` to the `a` tag containing the logo.