DOC: add doc strings to a lot of classes, update Copyright

src/main/java/org/caosdb/server/CaosDBServer.java

...n/java/org/caosdb/server/database/BackendTransaction.java

...ava/org/caosdb/server/database/access/AbstractAccess.java

src/main/java/org/caosdb/server/database/access/Access.java

...end/implementation/MySQL/MySQLDeleteEntityProperties.java

...backend/implementation/MySQL/MySQLDeleteSparseEntity.java

...ckend/implementation/MySQL/MySQLGetDependentEntities.java

...ackend/implementation/MySQL/MySQLGetFileRecordByPath.java

...tabase/backend/implementation/MySQL/MySQLGetIDByName.java

...end/implementation/MySQL/MySQLGetUpdateableChecksums.java

...ckend/implementation/MySQL/MySQLInsertEntityDatatype.java

...end/implementation/MySQL/MySQLInsertEntityProperties.java

...backend/implementation/MySQL/MySQLInsertSparseEntity.java

...ckend/implementation/MySQL/MySQLRetrieveCurrentMaxId.java

...backend/implementation/MySQL/MySQLRetrieveProperties.java

...se/backend/implementation/MySQL/MySQLSetFileChecksum.java

...implementation/MySQL/MySQLSetQueryTemplateDefinition.java

...database/backend/interfaces/RetrieveCurrentMaxIdImpl.java

...er/database/backend/transaction/RetrieveCurrentMaxId.java

src/main/java/org/caosdb/server/datatype/ReferenceValue.java