Pass environment variables from process environment and set up with flatpak environment.

Plasma Mobile docs suggest using flatpak for development.(https://docs.plasma-mobile.org/AppDevelopment.html) In the docs, they mention using environment variables to test how it looks/works on mobile devices. This doesn't work as expected in KDevelop because the environment configured in KDevelop is not passed on to the flatpak command that runs the app. This patch takes the environment variables set on the Process object being passed to flatpak runtime and passes them to the flatpak command.