Bumped neo4j-core version to 3.0.0.alpha.13

Cleanup Rakefile
Wrapped add_label and remove_label from neo4j-core, closes #331
Temporary disable JRuby on Travis because Rake neo4j:install is broken, #348
Check if travis jruby problem can be reproduced twice #348
Trying with jruby.launch.inproc to solve JRuby Neo4j Server installation on travis #348
Merge branch 'master' into orm_adapter