Created by: kmiyashiro
If you call collapse('hide') on a collapsable element that is already hidden, the transitioned event will never fire and therefore the complete callback will never run. That means the element's transitioning property will always equal 1 and it will be unresponsive to future collapse() calls.
This pull request adds a check for the in class to determine whether or not to show/hide an already shown/hidden element. This is potentially a breaking change if people rely on "shown" events for elements that are already shown... but this would be more consistent with the tab behavior where you can't show an already shown tab. Would be nice if we can add the state to the data so we don't have to check on the class.