Create Speaker profiles

[jrrickerson]

Add fields to the Speaker model and create a speaker profile view. This view should be available via an unauthenticated link from any Talk view so that visitors interested in a talk can see more information about that particular Talk's speaker.

Consider adding the following profile information fields:

• Speaker image / headshot
• Company / Organization name
• Website link
• Social media links (Twitter, Github, LinkedIn, etc)
• Public email address (NOT the user registration email address)
• Bio

See us.pycon.org for examples:
https://us.pycon.org/2017/speaker/profile/1390/
https://us.pycon.org/2017/speaker/profile/540/
https://us.pycon.org/2017/speaker/profile/2217/

Depends on #19