SP-475, BIS-255: first version done.

...cisd/openbis/dss/generic/shared/content/ContentCache.java

...isd/openbis/dss/generic/shared/content/IContentCache.java

...enbis/dss/generic/shared/content/IPersistenceManager.java

...dss/generic/shared/content/RemoteHierarchicalContent.java

...eric/shared/content/SimpleFileBasePersistenceManager.java

...ed/content/AbstractRemoteHierarchicalContentTestCase.java

.../openbis/dss/generic/shared/content/ContentCacheTest.java

...content/RemoteHierarchicalContentNodeMultiThreadTest.java

...ric/shared/content/RemoteHierarchicalContentNodeTest.java

...generic/shared/content/RemoteHierarchicalContentTest.java