Optimize 'electronize start' faster

[GregorBiswanger]

Install npm packages only for one time.. possibly on 'electronize init'?!

[robertmuehsig]

"init" ist currently only used for the manifest file and "init" currently doesn't know anything about the target platform that we want to run and it doesn't know the obj/desktop folder construct, so... this would be not a good fit IMHO.

But: We can make the build and start command much smarter. In theory (with a bit of risk of course), if we detect the npm_modules folder, we may just skip npm install.

At first I need to do this one: #7

The rest of the idea is discussed there.

[robertmuehsig]

Maybe not ideal, but if we detect the node_modules folder, we skip npm install... which speeds things up.