Implement level system to have new users catch up with older players

[marcianosr]

Levels should be leading and one of the pillars of trustworthyness.

• Exp. points are earned by answering polls (all based on current level):
  • Participating grants points
  • Answering correct grants points
  • Poll submits grants points
  • Multiple choice grants more points
  • Difficulty of the question adds possibly more points: [easy = * 1.25, normal = * 1.5, hard = * 1.75, intense = * 2] #92
• Level 1: 12 exp. Level 10: 100 exp
• Visually, the users are shown with avatars and a small progress bar displaying how much they need to proceed to the next leven (pokemon)

Criteria:

• All exp. points are rounded, no decimals