OAK-805 - Support for existing Jackrabbit 2.x DataStores

Refactored the implementation

-- Added a new method in BlobStore to obtain inputstream for given blobId.
    By default it is implemented using BlobStoreInputStream
-- DataStoreBlobStore uses the InputStream obtained from DataStore
-- Added support for inlinig binaries is there size is small

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1577448 13f79535-47bb-0310-9956-ffa450edef68