Do not be explicit about pressing Asset typeData

Being explicit about `Asset.typeData` upon page pressing was causing `nulls` to appear in the `pressed.json` `typeData`. This was causing a problem during parsing as we are expecting a `Map[String, String]` on parsing.

This lines up the types in pressing and parsing by outputting the `Map[String, String]` from the `Asset` directly.

@gklopper 
In this instance of the cartoon, there was no `caption`, and it was appearing as `null` in the `typeData` `Map`.