currencies: introduce BTC

Signed-off-by: Pierre-Alexandre Meyer <pierre@mouraf.org>
release.sh: initial import

Signed-off-by: Pierre-Alexandre Meyer <pierre@mouraf.org>
pom.xml: updates for release 0.7.11

Update killbill-oss-parent version to 0.5.14

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