Change of logic to serialize solution vector if only scalar variables are present. Issue #4249
Include ScalarCoupleable in inheritance of Function.  Refs issues #4267

Added default thread id of 0 as part of issue #4267 .
Merge pull request #4272 from mellis13/aux_scalar_function

Include ScalarCoupleable in inheritance of Function.
Merge pull request #4252 from mellis13/devel

Fix to aux system serialization logic
Merge commit '1a26300d3eb1f93977aca6cb638ab83fb88ead61'