Fix: several bugs in all Thresholds for log pruning after the refactor which has separated
 log pruning strategy and thresholds

Added method init() to Threshold interface to notify when a new pruning check begins

Add tests for FileSizeThreshold, FileCountThreshold, TransactionTimespanThreshold
Fixed copy/paste bug in PCL
Better assert message in PTC
Merge pull request #2654 from jakub-/transaction-terminate

Add Transaction.terminate() to the Transaction API
Makes server ITs use TargetDirectory instead of temp
Merge pull request #2658 from davidegrohmann/fix-log-pruning-bugs

Fix: several bugs in all Thresholds for log pruning
Support for interrupting transactions via the transactional REST endpoint

o Ensure ThreadToStmCtxBridge.getTopLevelTransactionBoundToThisThread() does not throw when interrupted [FIX]
o Rename assertInTransaction to assertInUninterruptedTransaction all over the place
o Changes TransactionRegistry: Now uses an ActiveTransaction marker per tx instead of a singleton
(needed to hold a reference to the tx such that we can interrupt it from a different thread)
o Adds number of transaction interrupts to TransactionMonitor

Signed-off-by: Andres Taylor <andres.taylor@neotechnology.com>