* delete transactions after block is written
* cleanup transaction_exists
* check for duplicate transactions
* delete invalid tx from backlog
* test duplicate transaction
* add timestamp to transaction assignment
* add reassignment delay to configuration
* refactor to multipipes
* # This is a combination of 7 commits.
# The first commit's message is:
stale transaction monitor and tests
# The 2nd commit message will be skipped:
# simplify logic
# The 3rd commit message will be skipped:
# node will assign to self
# The 4th commit message will be skipped:
# block listens for insert and update
# The 5th commit message will be skipped:
# more test coverage
# The 6th commit message will be skipped:
# test coverage
# The 7th commit message will be skipped:
# test coverage
* stale transaction monitor and tests
* update operation only returns new value
