ISPN-3921 Soft-Index File Store: (local files)-based cache store

- see SoftIndexFileStore javadoc for design info

https://issues.jboss.org/browse/ISPN-3921

I will provide performance comparison with LevelDB soon.

Currently the SoftIndexFileStoreFuctionalTest#testStoreAsBinary fails, but this bug in the test (should be fixed in another JIRA). The test does not purge the cache, therefore, when it configures the ByteArrayEquality to be used and store finds String key, it passes it to the Equality and the test fails.
It'd be nice to clarify what a 'node' refer to