Previously the implementation of isKnownDescription didn't cover all
possible messages that could be parsed and this caused null pointer
exceptions with certain messages. This now handles all the
possibilities.
This resolves: https://smartthings.atlassian.net/browse/DVCSMP-2227
Currently these DTHs return null when they parse a message that they
don't have specific handling for. This ends up sending the message up
to the cloud as an event, which prevented us from potentially parsing
that message in the cloud. By instead returning an empty map we can
instead send the message up to the cloud to be parsed there. This
allows us to add handling in the cloud for new message without requiring
and AppEngine deploy for them to work.
This resolves: https://smartthings.atlassian.net/browse/DPROT-200
