Cleanup implementation of `http_react` and `json_react`
Cleanup implementation of `http_react` and `json_react`

These Webparts share most of the functionality, with the main
exception being the conversion of the form data to the event argument.

It is possible to share their code by abstracting the conversion.

unipi-itc/Suave.EvReact,unipi-itc/Suave.EvReact,unipi-itc/Suave.EvReact