Add accessors to Geronimo transaction manager

The current geronimo transaction manager (version 3.1.4)  is not able to provide the start of transaction timestamp.

Also, retrieving the transaction timeout timestamp requires reflection that we want to avoid.

The patch should add accessors to the TransactionImpl class, like:

• getTimeoutTimestamp -> returns the timestamp corresponding to the timeout limit
• getStartTimestamp -> returns the timestamp of transaction start
• getTimeoutDurationInSeconds -> returns the maximum transaction duration in seconds