fix for STANBOL-1342: The Entity Co-Mention engine now uses a ServiceTracker for LabelTokenizers; In case the LabelTokenizer is not able to tokenize the selected text of a TextAnnotation it will be ignored (not considererd for co-mention detection); Minor: removed the custom ServiceReference Comparator from the MainLabelTokenizer as ServiceReference is anyway compareable

git-svn-id: https://svn.apache.org/repos/asf/stanbol/branches/release-0.12@1597063 13f79535-47bb-0310-9956-ffa450edef68