Support new UI theming options from v8.8

[jack-mil]

Version v8.8.0 and v8.8.1 of Notepad++ introduce some new "DarkMode" UI theming options.

See: Release Notes

A major addition is the ability to use an accent color for toolbar icons. We could decide on a single accent color to provide as default, with instructions on how to change it. Or provide versions of the config for all Catppuccin accent colors.

Exerts from release notes:

• Dark mode enhancements: combobox, slider, treeview edit, inactive menu bar & toolbar chevron.
• Add option to apply different color to fluent toolbar icons

I'll look into the new theming options, end experiment with how they look.

Edit: I will try and test backwards compatibility with older Notepad++ versions. If they have implemented things nicely, the presence of extra, unknown options might be a non-issue (simply ignored). Either way, some mention in the README/docs that some features of the theme may require the latest Notepad++ is probably a good idea.

[jack-mil]

Supporting the new options may be related to Issue #70

[jack-mil]

Update: The Dark mode enhancements are not new styles, just fixes to make darkmode UI look better. Nothing to do on our part.