Experimental RPM support and restructuring of installer-linux

This commit introduces RPM packaging for Neo4j.  It also moves around
the Maven module hierarchy to collect all the linux packaging under
installer-linux.

The RPM's are built from a Maven plugin and depend on 'rpmbuild'.

Yum handling and signing will be done later.

I'm pushing this PR out now because
a) it's Friday
b) I want early feedback

Feedback welcomed.

Going into the 1.9 branch because of Conways's law and because I'd like some feedback from production users (assuming they can safely test this in a non-production environment).