Upgrade to newer package versions

Newer React, newer tools, replace gulp-connect with gulp-webserver
because the former is deprecated.
Drop gulp-clean in favor of del

`del()` usage as per
https://github.com/gulpjs/gulp/blob/master/docs/recipes/delete-files-fol
der.md.
Whoops, forgot del dependency and require
Merge pull request #10 from ilkka/upgrade-libs

Upgrade to newer package versions