added accessor for the unique numeric layer id
_container => _root
first version of LayerControl
common style definitions
PropertyChangeEvent takes source parameter
LayerControl listens to layer events and property events
test cases for layer control
feature: placing of map controls with placeAt()
adding layout for map viewport, contols panel and layers
added a demo map application
building js for demo
hack: layer is only displayed after the first mouse click

Not fixed yet in js, but looks better that way in Dartium.
updated documentation
release 0.0.2
Merge branch 'work'