Bug fix in BaseTextualAnnotationParser.read()

* when MODALITY field is missing, add provided one (or dummy one "" if
it is not provided)
* also, labels are no longer converted at load time
New CLI to compute label similarity matrices
Bug fix in case file format does not contain a modality field
New .tvm and .tvt parsers
.tvt (resp. .tvm) support added to LabelMatrixParser (resp. AnnotationParser)
New REPEREScoresParser (.repere format with confidence score)
Faster implementation of FACETRACKSParser

uses new class method Annotation.from_df
Bug fix when extracting label subset

removed remaining ref to old API