BO3: multi-valued SourceBlock

BO2s have had the ability to handle multi-valued sourceblock so I
figured BO3s should be able to do it too
Corrections and Some additions for PR #181

@Override Annotation
Changed any ```ex.printStackTrace()``` calls to
```TerrainControl.log(Level.SEVERE, ex.getStackTrace().toString()```
Merge pull request #181 from Timethor/feature-bo3-multi-SourceBlock

BO3: SourceBlock can have multiple values