Reimplement XML chunker
- initially implemented for mediawiki xml
- missing features with regards to recursive elements, header replication etc.
(from redmine: issue id 1306, created on 2019-05-20tgradl)
- Relations:
- child #1188
- child #1300
- child #1305
(from redmine: issue id 1306, created on 2019-05-20tgradl)