Installing new map themes offered via Get Hot New Stuff (GHNS) is very inconvenient in the Qt-only version of Marble, because new map themes have to be downloaded from a web site as an archive which has to be extracted in a certain directory. In comparison, the KDE version of Marble offers a dialog where maps can be installed and deinstalled directly within the dialog.

Unfortunately, the dialog used in the KDE version has a dependency on kdelibs, which means that it can't be reused in the Qt-only version. Therefore, a new dialog class has to be implemented to offer the same convenience to users of the Qt-only version. Fortunately, however, there is already a class named NewstuffModel in the Marble source code which takes care of 1) listing map themes available via GHNS and which allows for 2) installation and 3) deinstallation of these maps. All that's missing is a widget for that class which shall allow users to perform these three actions and which shall be implemented in this task.

For convenience of use, the list of downloadable map themes should have a install/deinstall button next to each map theme, similar to the KDE version.

Reproducible: Always

Steps to Reproduce:
1. Click File -> Download maps... in the Qt-only version of marble (marble-qt)
Actual Results:  
A browser is opened which displays available map themes for download as archives.

Expected Results:  
A dialog should show up which lists map themes from GHNS and which shall allow for installing/uninstalling these map themes by a click of a button.

You can (and should!) use my branch at [https://github.com/shentok/marble/tree/MapThemeDownloadDialog] where I've done some initial work on this task.