MAX! binding improvements

* Discovery of multiple Cubes on the network
* Integration of MaxCubeDiscover.java into MaxCubeBridgeDiscovery.java for faster discovery results
* Improvement of discovery via mulicast message https://github.com/openhab/openhab/pull/1902
* Implementation of refreshType command to trigger refresh
* Change the numeric values types to BigDecimal to enable (once issue #64 fixed) direct reading of the default values
* Rearrange the device dispose to avoid confusing messages
* Fix no bridge found issue after changing the bridge configuration

Signed-off-by: Marcel Verpaalen <marcel@verpaalen.com>