Will lazy find avatar instead of injecting them into the conversation markup, #24

  - Will cache avatars from 3rd party in convos server
  - Add /avatar/:id resource
  - Add avatar() helper
  - Add "cache" attribute to Convos.pm
  - No need for storing "avatar:$id" in redis
  - Converted image/avatar-convos to jpg to make it compatible with 3rd
    party avatars

  Idea: Bundle avatars for irc.perl.org, freenode and "loopback". This
  can be easily fixed by appending an extra directory to the
  Mojolicious::Static object "cache".
Fix t/chat.t by fixing render_conversation() ordering bug, #24
Merge pull request #31 from Nordaaker/feature/24-avatar-lookup

Feature/24 avatar lookup