release textgrid-clients with listAggregation() method

tgrep portal uses a method listAggregation() which is in textgrid-clients:3.4.1-SNAPSHOT from the es6 branch. before releasing tgrep portal a release of textgrid-clients would be good, to only have stable dependencies. possibly just backport this one function.

and update cxf dependencies of textgridclients: http://cxf.apache.org/security-advisories.data/CVE-2019-17573.txt.asc?version=1&modificationDate=1579178542000&api=v2