Modify embed_favicon.py to pass HTML file name (or use
bin/FC_pregmod.html by default) to embed favicon into. An HTML
header for the story format was replaced by a format.js file, and
therefore we can't embed favicon there anymore, hence we switch
over to the story file itself.

Closes #461.

This reverts merge request !3010

Closes #246.

Favicons are embedded at the end of the header to avoid pushing the meta charset past the 1024 byte mark.