support preloading babel plugins without standardized name

[mnaamani]

This patch add support for electron-compiler to preload babel plugins that do not use a standardized name as the the npm module name, for example react-hot-loader

This indirectly helps to solve an issue when using electron-prebuilt-compile in an electron project and some npm dependencies are npm linked to a local "development package". When electron-compile can't preload a plugin defined in .compilerc babel-core ends up trying to locate all the plugins in the development package directory, and fails with an exception.

[anaisbetts]

I'll have a look at this in a bit, thanks for the PR

[mnaamani]

I hope it will prove useful, and it's a pleasure to contribute to a great project.

Let me know if you need any clarification on any anything

[anaisbetts]

Looks good! Sorry this took forever. I have one more PR to review then I'll put out a release