Implementing scheduled transactions. Not tested yet.
Also fixed the deadline not being registered.
Also added documentation to all *Transaction classes.
Fixed clone() method for BidirectionalTransaction and implemented missing clone() implementation in the Scheduled versions of the transactions

Typo
Now passing the current round number in argument to players. @TODO: Refactor them
Refactored + minor change to DummyPlayer. Tested, working
Forgotten arguments
Handy str representation for logging and debugging
Added a new player type, a cheater that will...well, try to cheat
Randomly selecting between cheaters and dummy ones
Transactions security implementation:
 - The players now do not have access to the Transaction object at any
   time (this avoids them changing the classes' methods... or the
   objects themselves)
 - We now ask the players for agreement over the transaction before
   trying to validate it.
 - Improved the DummyPlayer and CheaterPlayer as a consequence, to
   answer the agreement checks
 - Banning a player does not end the game anymore.
Some English-language fix :)