SimEtheral 1.2.1

Mostly incremental improvements but I expanded the API a bit, so it gets a version bump. It also has some different default behavior.

Changes in this version:

• Added EtherealHost.setStateCollectionInterval() to configure how often
  state is retrieved from the ZoneManager and sent to the clients.
• Added TimeSource.set/getOffset() to make it easier for clients to configure
  how far in history they'd like time to represent. Defaults to -100 ms.
• Expanded ZoneManager's javadoc.
• Made StateCollector's idle sleep time configurable and exposed it as
  an EtherealHost property.
• Flipped the StateCollector's update loop to sleep when idle instead of
  only after a valid state collection was made.
• Added a ConnectionStats object to the NetworkStateListener that currently collects
  the average ping time, percentage of missed ACKs, and the average message size.
• Modified the StateReceiver to add message size stats to a Statistics tracker. This
  let's clients see the average and total message sizes.
• Modified the build.gradle to replace the JME version with a specific
  version instead of letting it float. I think alpha4 is generally
  the minimum accepted 3.1 version at this point.
  Did the same for all of the floating version references.