Message widgets are now inserted into the listView through the `rowsInserted` callback of the messages model.
Messages are processed in the GetMessagesTask and GetApplicationMessagesTask when fetching multiple new messages. Single new incoming messages are processed in ProcessMessageTask.
* add "automatic" theme
set the theme and icons based on the system theme
* update the default icons based on system theme
* update pyqt to 6.5.0 to get the colorSchemeChanged callback
* rename style to theme
* remove unused svg files for default theme
* ServerInfoDialog: update feedback colors in dark mode