Allow (suggest?) icons/stickies for hashtags

[ianb]

Once we have #12 we'll be showing the hashtags in various places, and iconography would help make them easier to track.

Entering icons is hard, but we could instead just let you associate them – then whenever a hashtag was used we'd also add the icon. Maybe we'd do it via a dynamically generated user-specific stylesheet (so no real updates have to be done to content). All hashtag links would become like <a class="tag tag-recipes">recipes</a>

[ianb]

Also would be fun for the favicon of tag pages

[ianb]

First I need to find a set of icons/stickies, which will itself serve as the basis for the matching system.

[ianb]

We don't have tags now, not sure what they'll look like if we revisit that.