docs: refactor library code templates

[vobu]

during a hackathon with @wridgeu @matz3 and @petermuessig, we discovered the somewhat outdated code examples that get revamped with this PR

[petermuessig]

There is some more work todo on the documentation here. We will need to review it carefully, but in general, it is important to get that re-newed.

[flovogt]

Will be covered in backlog item CPOUI5FRAMEWORK-551