Fix font/icon flicker on initial page load

[meganesu]

When the page first loads, there's a brief flicker of the sans-serif fonts and giant FontAwesome icons. This is probably because the fonts and icons aren't done being loaded. This issue is to remove that flickering effect.

Further investigation:

• Icon flickering only seems to happen when opening the built HTML (i.e., not in develop mode).
• Icon flickering only seems to happen in Firefox. Tested the live site in Safari and Chrome but couldn't reproduce, even when simulating a slower network speed. (Chrome suppressed rendering until the content was loaded, which Firefox doesn't seem to do.)

[meganesu]

Apparently this issue is referred to as "flash of unstyled content" (FOUC).