Consolidate Logos and update README header (#14136)

* Consolidate Logos and update README header

- Remove unused `logo-lg.png`, `logo-sm.png` and `logo-192.png`.
- Consolidate `favicon.svg` and `logo.svg` to just `logo.svg`.
- Remove Safari Mask icon, it seems to work fine with just `favicon.png` (no SVG support).
- Remove Fluid Icon. It only served Firefox and SVG works just fine there.
- Update customization instructions.
- Update README.md to use SVG icon, increase logo size and center it and badges.

* Update README_ZH.md

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

* Update README_ZH.md

Co-authored-by: 6543 <6543@obermui.de>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: techknowlogick <techknowlogick@gitea.io>

templates/base/head.tmpl

@@ -62,10 +62,8 @@
 			{{end}}
 		};
 	</script>
-	<link rel="icon" href="{{StaticUrlPrefix}}/img/favicon.svg" type="image/svg+xml">
+	<link rel="icon" href="{{StaticUrlPrefix}}/img/logo.svg" type="image/svg+xml">
 	<link rel="alternate icon" href="{{StaticUrlPrefix}}/img/favicon.png" type="image/png">
-	<link rel="mask-icon" href="{{StaticUrlPrefix}}/img/logo-safari.svg" color="#609926">
-	<link rel="fluid-icon" href="{{StaticUrlPrefix}}/img/logo-lg.png" title="{{AppName}}">
 {{if .RequireSimpleMDE}}
 	<link rel="stylesheet" href="{{StaticUrlPrefix}}/css/easymde.css?v={{MD5 AppVer}}">
 {{end}}
@@ -108,7 +106,7 @@
 {{else}}
 	<meta property="og:title" content="{{AppName}}">
 	<meta property="og:type" content="website" />
-	<meta property="og:image" content="{{StaticUrlPrefix}}/img/logo-lg.png" />
+	<meta property="og:image" content="{{StaticUrlPrefix}}/img/logo.png" />
 	<meta property="og:url" content="{{AppUrl}}" />
 	<meta property="og:description" content="{{MetaDescription}}">
 {{end}}