Fix apps being grouped by web-renderer process in start menu

[m-roberts]

Currently, all apps call web-renderer process, which means that these are grouped together in the start menu.
In order to prevent this, each "app" needs its own process to be considered distinct.

Therefore, we should review how best to achieve this.
One way would be to make 'web-renderer' a C++/Qt application library, and then to compile a new process for each as part of pt-os-web-portal-desktop.

Another option would be to explore PyQt's WebEngine functionality.