Add support for Everspring AD131

This is a plug-in dimmer module. It seems to be
identical to the AN142.
Add null checks to ZWaveDbProductFile

Both everspring/ad131.xml and everspring/an142.xml (and many others)
have a missing <Configuration> section. This causes a NPE while parsing
the database. I’ve fixed this in ZWaveDbProductFile#getConfiguration()
by returning an empty list instead. Same fix applies to
ZWaveDbProductFile#getAssociations()
Merge branch 'master' into everspring-ad131

Conflicts:
	bundles/binding/org.openhab.binding.zwave/src/main/java/org/openhab/binding/zwave/internal/config/ZWaveDbProductFile.java
Merge pull request #1556 from evansj/everspring-ad131

New z-wave device Everspring ad131, plus some NPE fixes