Natural whitespace handling for SBT configuration parser AKA 'no more blankies'

The idea is to remove limitation with blank lines in sbt file.

For backward compatibility only one method is modified -  EvaluateConfigurations.splitExpressions.
Most pull request contains test and sbt files.
The father of idea is  @gkossakowski, solution was implemented by @WarsawScala members in project https://github.com/WarsawScala/sbtchallenge
I will remove checking null. File always is set