Launch app in terminal when Terminal=true

When the desktop file has Terminal=true (e.g. htop), it should be launched in a terminal.

Instead of calling "kstart5 -- ", this calls "kstart5 --application " when and only when:

1. kstart5 is available
2. the desktop file is in XDG_DATA_HOME/applications/, not XDG_DATA_HOME/kglobalaccel/
3. we are launching the desktop file's main group, not other actions

BUG: 455117