.idea: remove duplicate killbill-plugin-api-invoice entry

Signed-off-by: Pierre-Alexandre Meyer <pierre@mouraf.org>
Trivial code reformatting.

Signed-off-by: Pierre-Alexandre Meyer <pierre@mouraf.org>
pom.xml: update killbill-oss-parent to 0.7.12

Signed-off-by: Pierre-Alexandre Meyer <pierre@mouraf.org>