Add Rexster configuration class.

Rexster (http://rexster.tinkerpop.com)  no longer depends on OrientDB, therefore this class needs to live with the OrientDB repository. The addition of rexster-core to the pom comes with provided scope as OrientDB does not need to package rexster dependencies (they are provided by rexster when OrientDB is deployed there).
Merge branch 'develop' into pr/2212
Added dependency with rexster-core
Revert "WOWCache: Fix to the generation of fileId"

This reverts commit 33f830415f757f018d193738d3dcc79e754c4597.