Don't display profile data if it doesn't exist.

Since we don't require the user to have a Website, GitHub or Twitter account
we shouldn't display links to said things if they haven't filled in this info.
Require users to fill in a bio.

Users should be required to fill in a bio when they attempt to edit their profile
or submit a proposal because asking speakers for a bio will be work.
Merge pull request #12 from burlingtonruby/profile-data

Don't display profile data if it doesn't exist