neon: Allow completely hiding linear progress indicator

packages/neon/neon/lib/src/widgets/linear_progress_indicator.dart

@@ -3,6 +3,7 @@ part of '../../neon.dart';
 class NeonLinearProgressIndicator extends StatelessWidget {
   const NeonLinearProgressIndicator({
     this.visible = true,
+    this.alwaysThere = true,
     this.margin = const EdgeInsets.symmetric(horizontal: 10),
     this.color,
     this.backgroundColor = Colors.transparent,
@@ -10,21 +11,24 @@ class NeonLinearProgressIndicator extends StatelessWidget {
   });
 
   final bool visible;
+  final bool alwaysThere;
   final EdgeInsets? margin;
   final Color? color;
   final Color? backgroundColor;
 
   @override
-  Widget build(final BuildContext context) => Container(
+  Widget build(final BuildContext context) => !alwaysThere && !visible
-        margin: margin,
+      ? Container()
-        child: SizedBox(
+      : Container(
-          height: 3,
+          margin: margin,
-          child: visible
+          child: SizedBox(
-              ? LinearProgressIndicator(
+            height: 3,
-                  color: color,
+            child: visible
-                  backgroundColor: backgroundColor,
+                ? LinearProgressIndicator(
-                )
+                    color: color,
-              : null,
+                    backgroundColor: backgroundColor,
-        ),
+                  )
-      );
+                : null,
+          ),
+        );
 }