Migrate babili-standalone to this repo (and rename to babel-minify-standalone)

Follow up on https://github.com/babel/babel/pull/6029 by moving `babili-standalone` from the babel-standalone repo into this repo.

Reuse the same Gulp + Webpack configuration - `require('babel-standalone/src/gulpTasks.js`) should work to pull in the shared Gulp tasks.

Current package.json: https://github.com/babel/babel-standalone/blob/master/packages/babili-standalone/package.json
Current Gulp script (from separate babel-standalone repo): https://github.com/babel/babel-standalone/blob/master/gulpfile.js#L89-L97
New babel-standalone Gulp tasks file: https://github.com/babel/babel/blob/7.0/packages/babel-standalone/src/gulpTasks.js