Write support for setable values

[ramack]

Some values are settable over the vbus and this should be supported via the OpenHAB binding. Those include

• SystemTime (writing time configuration as shown in https://github.com/danielwippermann/resol-vbus-java/blob/master/vbus-example/src/main/java/de/resol/vbus/example/customizer/Main.java)
• vacation mode?
• heating mode and vacation
• ALL configuration options?