Prepare repo for JCenter/Bintray artifact publication

[oliverlockwood]

A few aspects to this.

• LICENSE should be LICENSE.md according to convention, as I understand it.
• We need to use the gradle-bintray-plugin for publishing.
• As discussed with @balooo, the SCM prefix can be removed as this is a single-artifact Git repo.
• .cirrus is removed from the artifact's groupId.

This has been tested and version 0.9.0 successfully uploaded to JCenter (it's currently "pending"; uploads don't automatically being visible until you log on and press "publish".

[jsravn]

For #7