Latex button

Added Spoiler and Latex buttons to the quick reply and full editor. The Latex button uses the tex tag, which may be the preferable way to typeset math (remotely hosted, more stable, saves resources, blah blah). Let me know if there's any issues.

[tex]\mu\eq \frac{1}{2}[/tex]


@dbooksta. Tex tags were here and went away. I'm not sure why and I miss them. The spoiler tag remained behind but not the tex tags.