D15102: Update deprecated QAbstractItemModel::reset() to use {begin, end}ResetModel() instead

[Dag Andersen]

danders added a reviewer: leinir.

REPOSITORY
  R8 Calligra

REVISION DETAIL
  https://phabricator.kde.org/D15102

To: dcaliste, #calligra:_3.0, leinir
Cc: Calligra-Devel-list, cochise, vandenoever