Template improvements now that `.actor` folder is implemented on platform

[mnmkng]

• ensure all readmes (and dockerfiles?) are in root of template
• use separate file for dataset schema to make it clear what's actor.json and what's schema
• remove advanced JS syntax like optional chaining from Node.js templates to make them more readable for newbies
• use a little more varied inputs and outputs in getting started, not just numbers, it looks dull
• ...