FunctionManager: cleanup Default impl

src/function_manager.rs

@@ -17,12 +17,11 @@ pub struct FunctionManager {
 
 impl Default for FunctionManager {
     fn default() -> Self {
-        let mut vec: Functions = Vec::with_capacity(COLORS.len());
-        vec.push((
-            Id::new("Function Manager"),
-            FunctionEntry::default(),
-        ));
-        Self { functions: vec }
+        let mut d = Self {
+            ..Default::default()
+        };
+        d.push_empty();
+        d
     }
 }