Improve the loading animation and use it in multiple places

- Supersedes https://github.com/ppy/osu/pull/926.
- [ ] Depends on https://github.com/ppy/osu-framework/pull/817.

osu.Game/Graphics/UserInterface/LoadingAnimation.cs

@@ -1,15 +1,48 @@
 // Copyright (c) 2007-2017 ppy Pty Ltd <contact@ppy.sh>.
 // Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
 
-using osu.Framework.Graphics.Sprites;
+using osu.Framework.Graphics;
+using osu.Framework.Graphics.Containers;
+using OpenTK;
 
 namespace osu.Game.Graphics.UserInterface
 {
-    public class LoadingAnimation : SpriteText
+    public class LoadingAnimation : VisibilityContainer
     {
+        private readonly TextAwesome spinner;
+
         public LoadingAnimation()
         {
-            Text = "Loading";
+            Size = new Vector2(20);
+
+            Anchor = Anchor.Centre;
+            Origin = Anchor.Centre;
+
+            Children = new Drawable[]
+            {
+                spinner = new TextAwesome
+                {
+                    TextSize = 20,
+                    Anchor = Anchor.Centre,
+                    Origin = Anchor.Centre,
+                    Icon = FontAwesome.fa_spinner
+                }
+            };
         }
+
+        protected override void LoadComplete()
+        {
+            base.LoadComplete();
+
+            spinner.RotateTo(360, 2000);
+            using (spinner.BeginDelayedSequence(2000))
+                spinner.Loop();
+        }
+
+        private const float transition_duration = 500;
+
+        protected override void PopIn() => FadeIn(transition_duration * 5, EasingTypes.OutQuint);
+
+        protected override void PopOut() => FadeOut(transition_duration, EasingTypes.OutQuint);
     }
-}
+}