button: Support passing a param to a button click action using the clickedParam property.

Fixes #86
Make it possible to pass controller per tab definition.

This allows the metadata of a tab definition to pass `controller` property so tab pane may have a different controller
than the controller of the template the tab-panes component was called on.

Fixes #88
Items Action Bar: Actions can be defined without the ‘disabled’ method defined.
showcase: Indication that items action bar is a new component.
Release 0.6.0
Update README.md - registration is not required anymore
Register modal component via initializer so it can be looked up later by the container.

Fixes #89