Having seen an editor themes collection for the first time with frescobaldi-themes I realized that the handling of themes could greatly be improved.

The theme preview (in Preferences=>Fonts and Colors) is great, but the process of "importing" new themes is very poor: themes can only be imported one by one, and without any preview.

Instead I suggest:

• Add a preference for themes directories (including one for a number of select built-in schemes)
• Provide a TreeView browser listing all themes found in these (nested) directory trees
• Automatically preview the selected theme.
• (I think) Provide a button to "install/import" the selected theme(s)
• Place this theme browser in a tab that can be shown alternatively with the current theme editor.

Disclaimer: I haven't looked into the way Frescobaldi handles the themes internally yet.

@rkubosz