Markdown preview when composing threads/posts
Add min height to post preview (less jarring)
mark_post_as_visited only increases last_post_number_read
Replying to an email and websocket streaming marks posts as visited
Wrap hiccup-syntax in `html`
Merge branch 'md-preview'

Conflicts:
	app/assets/javascripts/client-prod.js
Merge branch 'stream-visited'