Simplify the build scripts

[stephanrauh]

The build and release scripts are becoming cumbersome. Since integrating the new showcase (which is in incubator phase), the complexity has become even higher. Let's move all the scripts to a common folder and simplify usage.

Todos:

• [x] write shell scripts for every major task
• [x] update the package.json to call these shell scripts
• [ ] write a documentation page
• [x] fix the release:lib script