semanticClass and HTML/XML changes

[infininight]

Couple quick changes:

• Adds semanticClass which organizes the themes into dark/light groupings in the theme menu.
• The HTML grammar is getting updated with some grouping changes which necessitated some changes to keep themes working, the XML grammar is also being updated to match.

Notes:

• XML grammar is live, HTML grammar will be in 24-48 hours. Nothing is being deployed to the updater until I do so as a batch at one time once a final testing pass of everything.
• There were some parts of the theme with scopes I don't recognize like meta.section.html.head, these don't work but I don't think they ever did with the standard grammar? I'm working to make meta.element contain the tag and it's contents but that won't make it in this pass.