Investigate collapsing multiple matches into one annotation

[johann-petrak]

From johann-petrak/gateplugin-StringAnnotation#14

This could be done by either dealing with priorities (e.g. only first entry from a list, only first list) and/or by adding features that contain information for all matches in a list.
It would be interesting if we could combine this with case variation matching if case-insensitive matching is performed.

Also, if we create many annotations, one each for a separate entry, maybe allow to create them AnnotationGraph style to simplify processing.