[import sql] allow to import of a data portion when importing from a database table

Description

Allow to import of a data portion (start/end rows and columns) when importing from a database table. Previously, the widgets to specify the data portion were shown but not taken into the account. With this MR they are properly taken into account when importing tables and they are hidden when a custom query is used where the use can specify the data region to read via SQL.

This MR also switches from using KMessageBox to KMessageWindow to show the errors like it is already the case in the file import dialog.

Conformity

• Changelog entry
• Unit tests
• Update INSTALL
• Downport
• Fix #659 (closed)

When external dependencies are removed

• Reporting to ...