Fix unintended uses of overlapping spans in SpanLabelView where necessary

[ChaseDuncan]

Issue 665 fix a bug which allowed the overlapping spans check in SpanLabelView to be gotten around
by using SpanLabelView.addConstituent(Constituent). This fix broke some code because there were instances of the overlapping spans flag being set to false, i.e. declaring an intent to not allow overlapping spans, but overlapping spans were still being used.

In order to close the ticket we simply set the flag to true in all of these cases. Doing so does not change the behavior of the code. Still, it should be determined what was actually intended in these cases and make sure that the code reflects what was intended.

These are the files which use SpanLabelView and were changed:

corpusreaders/src/main/java/edu/illinois/cs/cogcomp/nlp/corpusreaders/ereReader/ERENerReader.java md/src/main/java/org/cogcomp/md/BIOCombinedReader.java
md/src/main/java/org/cogcomp/md/BIOReader.java
md/src/main/java/org/cogcomp/md/ColumnFormatReader.java
md/src/main/java/org/cogcomp/md/MentionAnnotator.java