CouchbaseCacheManager closing

implement the close method and check closed status in all operational
methods of the manager.
guard against classloader leak + thread-safe isClosed

only retain a WeakReference to the ClassLoader and make isClosed flag
volatile for better thread-safety
error checking and skeleton implementations

skeleton implementation of getCache methods and createCache
fix unwrapping
first implementation of CouchbaseCache

crude initialization and close, isClosed() checking in operational
methods.
create cache + signal cache closed to manager
release of cacheManager in cachingProvider
dependency on java SDK 2.0.1
implemented specific CouchbaseConfiguration
introduce Bucket and Cluster in cache + logger
gitignore build/