Set up speaker pages

[Kriesse]

• a page for each speaker and their talk
• an index page for all speakers (/speakers)
• a smaller gallery component that shows all speakers (for the main landing page)
• the ability to have a speaker page "unpublished"
• the schedule should use the same data, so each speaker page needs a start and end time as well

[Kriesse]

@silkine Do you want to design a small gallery component that can be on the startpage of https://2018.jsconf.eu/?
If not that's cool too, it's not high priority – then we can just close this issue :)