Align import and export APIs with other toolkits (import and export `TEXT`)

[nikku]

Describe the problem you're having

Our import and export APIs are not aligned with our other toolkits, as they do not import raw text documents but parsed JavaScript objects. That causes causes issues for our users and may be dangerous for us, too.

Describe the solution

• [ ] Import and export APIs work on text basis, that means the document is decoded from a string during import and encoded to a string during export

Why should we do it?

• Users are used to text-based import APIs
• Text is a safe format to fiddle around with. Serialized we do not run into issues like leaking internal references.