Electron packaging tools aren't installed with production builds

[Opal Mitchell]

If you're creating a production build as part of a release process, you run npm install --production to skip all the development dependencies. The gotcha is that the Electron packaging tools get skipped as well. Those need to move out of the devDependencies section of the package.json file and into the dependencies section. Both the electron-packager and electron-prebuilt modules should move.

There's already an --ignore=node_modules/electron flag in the build process, so we don't have to worry about those packages making it into the released builds.