Messages delivered twice when MessageEngine.setSpeed() used

[remikey]

The MessageEngine is treated separately from other ClockListeners by JBotSim's Scheduler. Indeed, it calls MessageEngine.onClock() directly, before anything else, in order to make sure that all messages have been delivered before the round starts.
In most cases, everything works well.

However, when one tries to change the delivering rate of the MessageEngine (MessageEngine.setSpeed()), the MessageEngine registers itself to the Topology as a ClockListener. From that on, the MessageEngine is both called:

• at the start of each round;
• during the rounds in which the ClockListener mechanism expires.

Although seldom used, this incoherent behavior must be fixed.

Please keep the MessageEngine as a ClockListener so that it might be used as such by other schedulers.
Also, fix/improve/enhance any related feature in the process.

[remikey]

Merged into develop.
What has been done:

• bug fixed by:

  • keeping MessageEngine as a "special citizen" in the Scheduler: it is still called every round in order to decrement each message's delay.
  • deprecating MessageEngine.setSpeed() and redirect it to MessageEngine.setDelay(). This method sets the delay to be applied to future messages.

• Since MessageEngine now handles delays, DelayMessageEngine has been renamed into RandomMessageEngine.

  For each message, a random delay is uniformely chosen between 1 and MessageEngine.getDelay().

• AsynchMessageEngine now:

  • better handles applying random delays in FIFO and NONFIFO cases;
  • is documented.