added backwards compatibility for hilightgroups in old settings files

[Hirogen]

This pull request improves backward compatibility for highlight group and entry settings by adding support for legacy property names (with typos) when importing old settings files. It also updates JSON serialization for highlight groups to use a more consistent and modern approach. The most important changes are:

Backward compatibility for highlight settings:

• Added legacy properties (HilightGroupList and HilightEntryList) to the Preferences and HighlightGroup classes, respectively, to support importing old settings files that used incorrect property names. These properties redirect data to the correct properties and are marked as obsolete for future removal. [1] [2]
• Added legacy properties (HilightEntryList and HilightGroupList) to the Settings class to support settings files that had these lists at the root level. These properties redirect data to the correct location in Preferences and are also marked as obsolete.

JSON serialization improvements:

• Updated the SaveHighlightGroupsAsJSON method in ConfigManager.cs to use JsonConvert.SerializeObject with indented formatting and UTF-8 encoding for more consistent and readable JSON output.

Dependency and import updates:

• Added missing using statements for highlight-related classes in Settings.cs to ensure all entities are available for serialization and deserialization.