feat(theme): add UiStyles.custom_icons hashmap

Signed-off-by: Sandro-Alessio Gierens <sandro@gierens.de>

src/theme/default_theme.rs

@@ -1,5 +1,6 @@
 use nu_ansi_term::Color::*;
 use nu_ansi_term::Style;
+use std::collections::HashMap;
 use std::default::Default;
 
 use crate::output::color_scale::{ColorScaleMode, ColorScaleOptions};
@@ -120,6 +121,8 @@ impl UiStyles {
             control_char: Red.normal(),
             broken_symlink: Red.normal(),
             broken_path_overlay: Style::default().underline(),
+
+            custom_icons: HashMap::new(),
         }
     }
 }

src/theme/ui_styles.rs

@@ -1,4 +1,5 @@
 use nu_ansi_term::Style;
+use std::collections::HashMap;
 
 use crate::theme::lsc::Pair;
 
@@ -29,6 +30,8 @@ pub struct UiStyles {
     pub control_char:         Style,  // cc
     pub broken_symlink:       Style,  // or
     pub broken_path_overlay:  Style,  // bO
+
+    pub custom_icons: HashMap<String, char>,
 }
 
 #[rustfmt::skip]