Add group in config file
This adds group to the config file.
Instead of putting everything under the "General" group we now organize things a bit better. This adds 2 more groups:
- "Appearance"
- "Plugins"
following more or less the tabs inside settings. More groups could be added in the future if needed.
This will "break" some config, the user will have to reenable their plugins and modified their appearance as they wish. However, this does not break the core parts; storagePath, default note name, etc, are untouched.