feat: begin implementation of "sub tabs"

src/common/tab_info.rs

@@ -2,13 +2,34 @@
 pub struct TabInfo {
     pub text: String,
     pub path: String,
+    pub sub_paths: Vec<SubTabInfo>,
 }
 
 impl TabInfo {
-    pub fn new(text: impl Into<String>, path: impl Into<String>) -> Self {
+    pub fn new(
+        text: impl Into<String>,
+        path: impl Into<String>,
+        sub_paths: Option<Vec<SubTabInfo>>
+    ) -> Self {
         Self {
             text: text.into(),
             path: path.into(),
+            sub_paths: sub_paths.unwrap_or_default()
         }
     }
-}
+}
+
+#[derive(Debug, Clone)]
+pub struct SubTabInfo {
+    pub text: String,
+    pub path: String,
+}
+
+impl SubTabInfo {
+    pub fn new(text: impl Into<String>, path: impl Into<String>) -> Self {
+        Self {
+            text: text.into(),
+            path: path.into()
+        }
+    }
+}