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>

snap/snapcraft.yaml

@@ -6,7 +6,7 @@ description: |
   an independent binary distribution across ALL platforms that Go supports,
   including Linux, Mac OS X, Windows and ARM.
 
-icon: public/img/logo-lg.png
+icon: public/img/logo.png
 confinement: strict
 base: core18
 adopt-info: gitea