Convert native GHC build of codeworld-api to use jsaddle instead of blank-canvas

Currently, the native GHC build of codeworld-api depends on blank-canvas, which has very limited support for JavaScript events and expressions. Instead, I'd like for it to use jsaddle, which can run a much wider set of JavaScript expressions on the client. This should allow a lot more code sharing between the two builds.

Some problems this will solve:

1. The `codeWorldLogo` picture will work in native mode.
2. The `TextEntry` event constructor will work in native mode.
3. Multiuser (`groupActivityOf`) programs can work in native mode. This will require that the host process link in code for the relay server, as well.

Comienza comparando el build nativo de GHC de codeworld-api con el otro build y localizando su integración con blank-canvas. Sigue las rutas de código para codeWorldLogo, TextEntry y groupActivityOf, y determina después cómo enlazaría el proceso host el código de relay-server; se considera terminado cuando estas funciones funcionan en modo nativo sin blank-canvas.

Escrito por el modelo de indexación a partir del texto del issue.