Add Activateable Concern #39

Creates a concern for managing lifecyles without deletions. Classes can
have an enum activated_state set to either :active or :inactive and can
declare that certain relations should proxy the parent classes' state.
Add enable! and disable! to memberships
Extract resource activation to a seperate object
Move activation of lib add lib to autoload
Merge pull request #42 from edpaget/disable_users

Add Activateable Concern #39