D11603: Update katepart docbooks to 18.04

[Burkhard Lück]

lueck added a subscriber: kwrite-devel.

REPOSITORY
  R40 Kate

REVISION DETAIL
  https://phabricator.kde.org/D11603

To: lueck, #kate, #documentation
Cc: kwrite-devel, kde-doc-english, michaelh, kevinapavew, ngraham, demsking, 
cullmann, sars, dhaumann