contributing.md doc love

- link to download VirtualBox 4.3.20 needs to be updated
- fix/update broken image oh how to download binaries and extensions
- update reference to coderwall_v3
remove unused queues

- search_sync is staying around for now, because of how job uniqueness
is implemented
- seems like a good idea to also keep ‘default’ around even though no
worker/job uses it.  It is the default queue that sidekiq uses. So just
a smart move to keep it around?
- remove all other unused queues
Change route precedence of user_protips to come before slug_protips
Merge pull request #251 from codebender/contributing_love

contributing.md doc love
Merge pull request #254 from nicolasiensen/bounty/418

Quick fix the user protip route #418
Fixed error in the Octopussy badge
Reference user off team members
Merge pull request #252 from codebender/remove_old_sidekiq_queues

remove unused queues