Add plugin option to automatically add JS executable as a resource

[altavir]

The next step for #148.

This requires three things:

• Specify the name of the bundle JS (and maybe css) like this:

    js{
        browser {
            webpackTask {
                this.outputFileName = "js/jupyter-bundle.js"
            }
        }
        binaries.executable()
    }

• Add resource dependency on the bundle like

    afterEvaluate {
        val jsBrowserDistribution by tasks.getting

        tasks.getByName<ProcessResources>("jvmProcessResources") {
            dependsOn(jsBrowserDistribution)
            afterEvaluate {
                from(jsBrowserDistribution)
            }
        }
    }

• Add the resourceFromJsTarget function in the resource builder to load a class-path resource.

Willing to contribute to this one as well as soon as I have time.