When running a bundled application, the backend is forked. But any
command line parameter passed to the Electron application isn't passed
down to the backend. This commit makes sure that relevant arguments are
passed to the forked backend process.

Signed-off-by: Paul Maréchal <paul.marechal@ericsson.com>

When forking, Electron 4 forgets to set `process.versions.electron` in
the sub-process, making some packages wrongly guess their environment.
This commit manually patches this variable.

Signed-off-by: Paul Maréchal <paul.marechal@ericsson.com>

The generated application code is not forking the backend when working
from sources. Running the backend in the Electron main process was only
meant to help with debugging. This commit makes the generated code fork
the backend unless a `--no-cluster` flag is specified.

Signed-off-by: Paul Maréchal <paul.marechal@ericsson.com>