WIP: EHN: version history

src/main/java/org/caosdb/server/database/DatabaseUtils.java

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

...end/implementation/MySQL/MySQLRetrieveVersionHistory.java

...backend/implementation/MySQL/MySQLUpdateSparseEntity.java

...rver/database/backend/transaction/InsertSparseEntity.java

...abase/backend/transaction/RetrieveTransactionHistory.java

.../database/backend/transaction/RetrieveVersionHistory.java

...ver/database/backend/transaction/RetrieveVersionInfo.java

...sdb/server/database/backend/transaction/UpdateEntity.java

...rver/database/backend/transaction/UpdateSparseEntity.java

...n/java/org/caosdb/server/database/proto/SparseEntity.java

.../org/caosdb/server/database/proto/VersionHistoryItem.java

src/main/java/org/caosdb/server/entity/Entity.java

src/main/java/org/caosdb/server/entity/Version.java

...va/org/caosdb/server/entity/xml/VersionXMLSerializer.java

src/main/java/org/caosdb/server/jobs/core/History.java

src/main/java/org/caosdb/server/transaction/Insert.java