added gulp.js with basic configuration to minify and concatenate Javascr...

I have tried Gulp.js to concatenate Javascript files and it seems to be simple and easy to use tool.

I think it's better to build a single Javascript files rather than using Javascript itself to load multiple files, which takes extra time and also can cause cross domain policy violations in some browsers if the examples are loaded without a webserver for example.

Right now this does not replace the file loading in Potree.js but is only a trial.
See the documentation how to run Gulp.js: https://github.com/Georepublic/potree/blob/feature-gulp/docs/build.md

(additional note: I created "develop" branch as well as this "feature-gulp" branch, so unfinished code does not get merged into "master".