only use attr_accessible if it's supported

Rails 4 doesn't define the ActiveModel::MassAssignmentSecurity constant,
but there is a gem that allows it to be used. The models will now only
try to use the functionality if the constant is defined
Use of these methods is preferred for Rails 4

The Relation#all method is deprecated as of Rails 4, we should use these
to acheive the desired behavior.

yep.
Merge branch 'rails-4/attr_accessible'
Merge branch 'rails-4/deprecation'