[jvstm-common] Added API to get a box value in a previous version
New Feature: Added API for Long Lived Transactions
[jvstm-common] Implementing Long Lived Transactions
[jvstm-common] Properly record the read set of a Long Lived Transaction
[long-tx-api] Improved the API to add elements to the read/write sets.

  * Adapted LongLivedTransaction to use the new API
  * Renamed attribute to slotName in LogEntry
[jvstm-common] Added a method to JVSTMDomainObject to return a VBox by its name

  * Also uniformized the format of the generated code for JSON handling
[jvstm-common] Proper support for Transactional Context commit
Optimizations...
[long-tx-api] Caching DomainSlotKey's hashCode
[jvstm-common] Only validate Long Lived Transaction if anything was written
[long-tx-api] Refactor: Read/WriteSet is now kept as a ValueType