Make index creation idempotent

IndexingService.createIndex now just does nothing if it is asked to create an index
that already exists. Instead of throwing an AssertionError. This makes it idempotent.
Move Cypher 1.9 parser into compiler package
Move Cypher 2.0 parser into compiler package
Move internal Cypher classes into internal package
Invalid package + unused imports
Merge pull request #1306 from cleishm/cypher-compiler

Move Cypher versioned parsers into compiler package
Merge pull request #1325 from chrisvest/schema-index-copying-in-ha

Make index creation idempotent
Add @Ignored ManyMergeStressTest for exposing lucene issue
Make sure label scan store readers are closed when their owning statement is closed