Add muted shaka images

Uploading four variations of "🤙" images:
black outline
white outline
solid black
solid white

In three different sizes:
20x20, @2x, and at @3x

Added contents.json imageset file

*They are only the images, I have not changed any code within the app.

Would you please add the images where they are needed? or point me in the right direction? I have much yet to learn.

I hope these are the versions you need. If there are any adjustments, please let me know.

Changelog-Changed: Added muted shaka images instead of thumbs up
Closes: #226

damus/Assets.xcassets/nostr-hello.imageset/Contents.json

@@ -0,0 +1,68 @@
+{
+  "images" : [
+    {
+      "filename" : "nostr-hello-outline-black.png",
+      "idiom" : "universal",
+      "scale" : "1x"
+    },
+    {
+      "filename" : "nostr-hello-outline-black@2x.png",
+      "idiom" : "universal",
+      "scale" : "2x"
+    },
+    {
+      "filename" : "nostr-hello-outline-black@3x.png",
+      "idiom" : "universal",
+      "scale" : "3x"
+    },
+    {
+      "filename" : "nostr-hello-outline-white.png",
+      "idiom" : "universal",
+      "scale" : "1x"
+    },
+    {
+      "filename" : "nostr-hello-outline-white@2x.png",
+      "idiom" : "universal",
+      "scale" : "2x"
+    },
+    {
+      "filename" : "nostr-hello-outline-white@3x.png",
+      "idiom" : "universal",
+      "scale" : "3x"
+    },
+    {
+      "filename" : "nostr-hello-solid-black.png",
+      "idiom" : "universal",
+      "scale" : "1x"
+    },
+    {
+      "filename" : "nostr-hello-solid-black@2x.png",
+      "idiom" : "universal",
+      "scale" : "2x"
+    },
+    {
+      "filename" : "nostr-hello-solid-black@3x.png",
+      "idiom" : "universal",
+      "scale" : "3x"
+    },
+    {
+      "filename" : "nostr-hello-solid-white.png",
+      "idiom" : "universal",
+      "scale" : "1x"
+    },
+    {
+      "filename" : "nostr-hello-solid-white@2x.png",
+      "idiom" : "universal",
+      "scale" : "2x"
+    },
+    {
+      "filename" : "nostr-hello-solid-white@3x.png",
+      "idiom" : "universal",
+      "scale" : "3x"
+    }	    
+  ],
+  "info" : {
+    "author" : "xcode",
+    "version" : 1
+  }
+}