Editorial: make th implied wording consistent with the style of td

[carmacleod]

Make th implied role wording consistent with the wording style of td implied role (and others)

• role first, then condition
• remove unnecessary mention of html-aam

Also - nit - make tr role=row implied role have same visual style as others

---

Preview | Diff

[scottaohara]

this is a bit of an overlap with #265, but i think that's fine as this doesn't change anything like 265 will.

i think this looks good, but just want to get the wording updated in the implementation report before i pull this in (otherwise i might forget to update that to match)