feat(selection): add selection class and spec
feat(selection): add api proposal methods
chore(observer): rename observer to observable
chore(gulp): save paths in variables
chore(extend): remove extend static method from classes
feat(utils): add support to get the injector from a given $element
chore(utils): support multiple source classes in extend method
chore(controller-dir): simply object
feat(decar-service): add angular decaf service with the class extensions
chore(tests): fix getting classes from decaf service
chore(example): update to use new extension API using $scope