[Devoxx crawler] Move some JSON config at the cfp.dev API level

[Frédéric Camblor]

@stephanj here is the list of attributes that I'd find relevant to move away from conference descriptor json file, so that each event can have control of it from cfp.dev website :

• Tracks: I'm currently missing themeColor attribute in cfp.dev's tracks field to use specific colors per track in the mobile app, hence I re-defined tracks in the descriptor presently

• Sponsors (see #13 with example here)
  

• Rating bingo choices (id + label), find an example here

• Social media entries for the event (see example here)

If you implement some of them, please mark the checkbox and give me an URL where I could retrieve this information so that I can update devoxx crawler impl accordingly