- Changed SpanLabelView.addConstituent(Constituent) to enforce nonoverlapping
  constituents when appropriate, i.e. the flag is set.
- Added a class with two basic tests to make sure that the changes work
  correctly.

- Moved inline comment into JavaDoc comment above class in SpanLabelViewTest
- Moved start, end variable initialization and overlap into conditional
  statement so that they only occur when overlapping spans are not allowed
- Moved SpanLevelViewTest into correct module

- Fixed multiple places in MD and one place in corpus readers where
  overlapping spans were implicitly or explicitly forbidden but still
  being used

- Added another ctor to TokenLabelView which has a parameter
  for specifying whether or not to allow overlapping spans
- Changed the TokenLabelView ctor which is used in StanfordTrueCaseHandler
  since it was clear that overlapping spans are desired