In order to specify your own sanitize method
Implemented .mass_assignment_sanitizer configuration option

Added an ability to specify your own behavior on mass assingment
protection, controlled by option:
ActiveModel::MassAssignmentSecurity.mass_assignment_sanitizer

Only one space is needed, yo!

This patch allows to specify the name of your models independent of the class name.

Attributes with :string type should not be given the type passed in model serialization options. Closes #1058

Now that we propagate the enabling/disabling to descendants, we no longer have to check the disabled_observer Set on each superclass of the model class.  This was causing a bug when disabling all observers at a superclass level and then enabling an individual observer at a subclass level.

Plus the logic is simpler now :).

Fix dev env memory leaks by using AS::DescendantsTracker rather than keeping track of subclasses manually.

There's also no need to keep track of all ObserverArray instances in a hash, as this is likely to leak memory, too.