Merge tag '0.6.80' into develop

Add FB remarketing pixel and custom events
Remove useless assets
Re-enable dashboard simple stats

See also https://github.com/potomak/tomatoes/commit/1aa081525d91cdf5f11d770b0dc0b5fe7796d912
Remove merit and badges

Queries to merit_actions collection are the slowest and should be
optimized.

Note: this is a temporary solution to MongoDB slow queries problems.

See the "Slow queries" section at MongoHQ admin panel to get more info
about those queries.

Slow query example:

  Score		87.7
  Frequency		32.65/hr
  Collection		merit_actions
  Count		13951
  Avg ms		2686
  Avg nscanned		590346
  Example Query	{ processed: false }
  Query Profile { processed: "$boolean" }
bump version number to 0.6.81
Merge branch 'release/0.6.81'