Messages with images or media were causing the scroll position to jump
around when they loaded, because rendering them changed the height of their
elements from 0 to full-height sometime after they were inserted into
the DOM.
Now when rendering attachments, we wait for them to load so they can
render at full height immediately, then warn our parent message list
before and after a potential height change, so the scroll position can
be saved and reset.
// FREEBIE
Simplifies the grunt watch task for sass. Renames sass partials with
leading underscores. Flattens stylesheet directory. The only remaining
raw css file is options.css.
Move globally-relevant styles to _global. Shrink overall font size.
