Add ability to open, edit, and save the family data file

[rafgugi]

Description

Currently, the app doesn't allow users to edit the family data except via the YAML file in the source files.

Expected behavior

• The YAML file in the resource files is just initial family data.
• Under the hood, open the initial YAML file as a text, then convert it to JSON programmatically. Instead of directly opening the YAML as JSON using the plugin. This YAML JSON converter will be used later.
• Add an "Open" button to open a YAML family data file.
• Add a textarea to show and edit the current family data.
• Add a "Save" button to save current family data.

Additional context

This feature would enable many users to use this same app without having to deploy themselves.