make electron runtime deps optional

[akosyakov]

fix #4871
fix #2758

[akosyakov]

It's ready for the review. Guys please have a look we need to fix theia-apps next images.

[kittaakos]

Your changes look good to me, however, I could not try it in a final, bundled application.

[akosyakov]

thanks @kittaakos, waiting for travis build and merging if no objections

[kittaakos]

merging if no objections

Sure, if I understood the issue, the theia-apps are broken anyway so that it won't be worse.

[akosyakov]

@kittaakos it will allow to fix them, i more worry about people who build electron products that we break them now :)

[thegecko]

LGTM