Tweak theme color to match the Godot editor's background color

This makes for a more seamless-looking address bar/status bar
when using the web editor on a mobile device, either directly
in the brower or installed as a progressive web app.

This also specifies a theme color for the web editor's offline
fallback.

(cherry picked from commit 7ef459c2d7)

misc/dist/html/editor.html

@@ -9,8 +9,8 @@
 	<meta name="apple-mobile-web-app-capable" content="yes" />
 	<meta name="application-name" content="Godot" />
 	<meta name="apple-mobile-web-app-title" content="Godot" />
-	<meta name="theme-color" content="#478cbf" />
-	<meta name="msapplication-navbutton-color" content="#478cbf" />
+	<meta name="theme-color" content="#202531" />
+	<meta name="msapplication-navbutton-color" content="#202531" />
 	<meta name="apple-mobile-web-app-status-bar-style" content="black-translucent" />
 	<meta name="msapplication-starturl" content="/latest" />
 	<meta property="og:site_name" content="Godot Engine Web Editor" />

misc/dist/html/manifest.json

@@ -6,7 +6,7 @@
   "start_url": "./godot.tools.html",
   "display": "standalone",
   "orientation": "landscape",
-  "theme_color": "#478cbf",
+  "theme_color": "#202531",
   "icons": [
     {
       "src": "favicon.png",

misc/dist/html/offline.html

@@ -4,6 +4,8 @@
 	<meta charset="utf-8" />
 	<meta http-equiv="X-UA-Compatible" content="IE=edge" />
 	<meta name="viewport" content="width=device-width, initial-scale=1" />
+	<meta name="theme-color" content="#202531" />
+	<meta name="msapplication-navbutton-color" content="#202531" />
 	<title>You are offline</title>
 	<style>
 		html {