Qt Designer: Add translation-attributes to string list properties.

- Add translation parameters to XML schema for ui.
- Introduce PropertySheetStringListValue to property sheet,
  load & save code, add to property sheet and property editor.

Task-number: QTBUG-8926
Task-number: QTBUG-20440

Change-Id: Ib5e9e2e9ba603bb68984a102e3c3fc8ff1cb4df0
Sanity-Review: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Jarek Kobus <jaroslaw.kobus@nokia.com>