.gitignore: purge obsolete entries
Mark the LuraWaveService as optional

With the recent change in SciJava-common's service infrastructure,
services that are expected to fail in certain setups need to be marked
by the Optional interface; otherwise, the log will contain a nasty
stack trace, reporting that the service could not be started up.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>