Make it easier to contribute

[julkue]

• Created build script in package.json. Why?
  • To only need to run one command to build the project
  • With that, gulp dependency can be used directly from node_modules folder and doesn't require a global installation
• Created a CONTRIBUTING.md for other to know what they need to do when they want to develop in the project
• Ignored default npm-debug.log files and PHPStorm/Webstorm config files

Closes #51

[erikwett]

The fact that you needed to run two gulp tasks to make a build was really a bug. A fix for that has been merged into the repository.

[julkue]

Alright, feel free to pick the things you need or close the PR entirely. I've already deleted the fork, so I currently don't have an intention to adjust something.