Migrate away from SQLite in App

[worldofjoni]

Storing the meal plans in the app for online use in a SQL database is not just rather complicated, it also slows the app down considerably: Most of the reloading time is not spent with querying the API but rather storing the returned data in the database, many queries have to be performed here.

As an alternative, I propose an object storage, where data is just stored like returned from the GraphQL API and used in the app, avoiding complicated data transformations. E.g. https://pub.dev/packages/objectbox

Maybe Persisted Queries are an option, they seem to be (somewhat?) supported in graphql_flutter (see here).

@AlexKutschera Thoughts?