Add Marketplace gallery banner config

Author: lumaxis

package.json

@@ -4,6 +4,10 @@
 	"description": "Easily copy snippets of code without unnecessary indentation, making it easier to share them e.g. via Slack",
 	"version": "0.1.1",
 	"icon": "images/icon.png",
+	"galleryBanner": {
+		"color": "#1C252C",
+		"theme": "light"
+	},
 	"preview": true,
 	"publisher": "lumaxis",
 	"author": {