Ensure all observers are removed when destroyObservable is called.
Include padding in flowed layout row sizes to avoid cutting off content.
Fixes improper implementation of SC.SelectionSet:constrain (fixes #870).

After cleaning up a memory leak in SC.Set, it was discovered that the constrain method of SC.SelectionSet doesn't work properly.  It was naively using forEach to iterate through the objects while mutating the array so that the last object would never be constrained.  Includes unit test.
Remove the dependent keys from some SC.MenuItemView properties.

Since these properties will be updated manually based on the configured
key, there is no reason to have a static dependent key specified.
Gets rid of deprecated code and warning on IE.
Remove element from SC.Event._elements if events for it cannot be found.

This prevents leaking memory in this case.
Bumping to SC 1.9.0.14.