Investigate how to support different versions of electron/OpenFin/browser

[JDawes-ScottLogic]

From the GoogleDoc:

Perhaps use peer dependencies for electron (allowing version flexibility)
See if we can fix it, or raise an issue

Determine how we support different versions of OpenFin, electron, and the browser, especially in the cases of breaking APIs etc.

[BenLambertNcl]

electron-download looks like something possibly worth looking into. Seems like it has similar functionality to the openfin-launcher package, in that we can specify a version to download. I think this would mean we could always include the @types/electron packages, but not 100% sure.

[JDawes-ScottLogic]

In relation to this, there's also a question of what version of node we need to be loading for the CI builds. Travis runs against node 4, 6, and 7, and Appveyor installs the latest (I think).

Do we need to be testing against different versions, or are we only using it for running tasks etc. so we can use a single version.