Changes the user under which the neo4j service runs as, under Debian

The file /etc/default/neo4j will be sourced and the NEO_USER variable
 discovered, defaulting to the value "neo4j". That is the user that
 the postinstall scripts assigns ownership of the installation files
 and now this is the user that the start-stop-daemon will start the
 process as.

 Also with refactorings in the init script, and removal of duplicate
 copies of the init script.

Fixes #1348 (https://github.com/neo4j/neo4j/issues/1348)

Refactorings to init script.

Refactoring: remove duplicate init scripts.