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/home.tmpl

@@ -3,7 +3,7 @@
 	<div class="ui stackable middle very relaxed page grid">
 		<div class="sixteen wide center aligned centered column">
 			<div>
-				<img class="logo" src="{{StaticUrlPrefix}}/img/logo.svg" />
+				<img class="logo" width="220" height="220" src="{{StaticUrlPrefix}}/img/logo.svg"/>
 			</div>
 			<div class="hero">
 				<h1 class="ui icon header title">