Allow local properties and introduce Component features.

Component:
 - add/removeLocalProperty(...), clear/getLocalProperties() added.
 - enable/displayLocalDisplayProperties(...) added.
Implement Tooltip as external feature (leave old interface).
Add Experimental ComponentHoverShape-feature.
Improve ComponentHoverPropertyFeature.

Component: Add PROPERTY_COMPONENT_ADDITIONAL_BACKGROUND_SHAPE.
Button: Use ComponentHoverPropertyFeature for hover effect.
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