Use ts-morph instead of Handlebars

[ffflorian]

ts-morph can create TypeScript with TypeScript. We should use it instead of using a template engine.

Pros

• Cleaner TypeScript code
• Staying in the TS world without reading external files
• No more manual comment building
• Handlebars is made for HTML

Cons

• A lot of work for no visible output
• There might be some TS expressions which are not supported by ts-morph yet (they need to be written manually then).