Added babel preset preloading

[hzlmn]

I think it is nice feature to have preloading of presets, based on parsing devDependencies.
So basically:

x.babel = function* () {
  yield this.source(file)
       .babel({ preload: true })
       .target(dist)
}

will parse devDependencies, find babel presets by regex and include them as available presets.
In this way we know that we have only one source of truth and we did not forget to include some presets

cc @bucaran @lukeed

[lukeed]

Cool cool 👍 I'm going to condense the code a bit, but otherwise looks great! Thanks!

[hzlmn]

@lukeed also, plugins could be preloaded in the same way.

[lukeed]

@hzlmn good call

[lukeed]

@hzlmn should we call this 1.0? 💭

[hzlmn]

@lukeed Yes, we can IMO 💎