Fix #19: visual separation of speakers.

There are a few changes in here, I got a bit carried away. Basically,
the speakers page looks a bit nicer :smile:  An overview of the changes:

 - Remove the inline headings in favour of Font Awesome icons where
   appropriate (i.e., a speaker's links).
 - Delineate the speaker's bio by separating it visually, slightly: no
   need for the "Bio:" heading.
 - Make the submitted sessions an h4, and list out the sessions in a ul.
 - Add 30px of space between speakers.

I'll add before and after screenshots to #19 so the two can be compared.