[backend-jvstm-common] Bugfix: Put initialValue on all VBoxes upon object creation

  * Otherwise, the VBoxes would not be correctly registered in the
    transaction's write-set (while still having the correct initialValue
    `null` in memory).  As such, they would not be written to the Repository
    upon commit.
[backend-jvstm-common] Improve logging

  * Improve some logging messages
  * Add new logging messages
  * Use hexadecimal format when logging OID values
  * Use DEBUG instead of TRACE for logging