failed to move acts_as_rateable to gem on first attempt

  Not maintained in 4 years. There's a gem but its init file
  is not compatible with rails 3.
  There are forks on github that fix this but they also apply
  other changes in particular they change the database structure
  possible next steps:
  * fork on github and cherry pick from other repos
  * use letsrate instead https://github.com/muratguzel/letsrate
  * include as lib in crabgrass
turn acts_as_rateable plugin into a lib
remove better_acts_as_tree from readme - not in use

Also we won't need the plugins_with_allowed_fixtures anymore
turn acts_as_versioned plugin into a lib