In Gibbs solver, added computation of sample mean and (co)variance for Real and RealJoint variables

For RealJoint (and Complex) variables, doing this computation is not done by default, but can be enabled via a configuration option.
Dimple options and environment changes:
 - MATLAB support for DimpleEnvironment
 - Moved DimpleEventListener from FactorGraph up to DimpleEnvironment
 - Fixed some bugs in MATLAB EventLogger
 - More tweaks to options implementation
 - Updated documentation for events package in Java
Merge branch 'master' of seymour.lyricsemiconductor.com:LyricLabsADI/dimple
Check for inability to check out Communications Toolbox license in MATLAB tests
Add another check for communication toolbox license failure