Move some artifact and attribute type methods to Blackboard

...ngs/java/src/org/sleuthkit/datamodel/AbstractContent.java

bindings/java/src/org/sleuthkit/datamodel/AbstractFile.java

bindings/java/src/org/sleuthkit/datamodel/Blackboard.java

.../java/src/org/sleuthkit/datamodel/BlackboardArtifact.java

...va/src/org/sleuthkit/datamodel/CommunicationsManager.java

...gs/java/src/org/sleuthkit/datamodel/OsAccountManager.java

bindings/java/src/org/sleuthkit/datamodel/Report.java

bindings/java/src/org/sleuthkit/datamodel/SleuthkitCase.java