Convert to typescript

[0xR]

This PR migrates to typescript. It also increases the type coverage. The code is easier to understand now.

It also fixes some long standing bugs resulting in { empty } graphql responses.

• [x] type conversion
• [x] fix eslint
• [x] fix tests
• [x] check example still works
• [x] ensure the graphql resolvers can deal with non json responses

[0xR]

Could you do a review @yarax

[yarax]

Really many changes, but LGTM and tests seem to be fine