Replace JSON editing with property editing for state machine designer

## Why you need it?
Currently, we allow users to edit properties by writing JSON directly. However it is a temporary solution for property editing. A more appropriate way would be the properties panel.

## How it could be?

A desired properites panel is something like the following,

## Other related information
Please merge related PR to the **refactor_designer** branch.

Review the refactor_designer branch and the related pull request mentioned in the issue, then compare the current JSON editing flow with the desired properties panel shown in the screenshots. Done means state machine properties can be edited through the panel instead of by writing JSON directly.

Written by the indexing model from the issue text.