Refactor AbstractCacheTransaction

There are several collections holding transaction related information in the AbstractCacheTransaction:

• lockedKeys: this holds all the keys that were actually locked on the local node
• affectedKeys: this holds all the keys that were acquired by the transaction allover the cluster
• backupKeyLocks: this holds all the locks for which the local node is a secondary data owner.

To do:

• affectedKeys belongs to LocalCacheTransaction(subclass) and no point in having it in the AbstractCacheTransaction
• a better name for affectedKeys might be "clusterLockedKey" and for lockedKeys --> localLokedKeys
• also add a Javadoc explaining the correlation between these key groups