Rework 'make generate-images' (#12316)

* Rework 'make generate-images'

- Remove external dependencies and replace it with a node script that
  does does the same.
- Move detail removal from gitea-sm.png to favicon.png
- Remove favicon.ico and its generation, it is unused and we already serve
  favicon.png in its place.

Fixes: https://github.com/go-gitea/gitea/issues/12314

* use proper centering value for preserveAspectRatio

* fix lint

* use fabric

* better linting fix

* fix typo

* mention detail-remove class in docs

assets/logo.svg

@@ -115,6 +115,7 @@
   <g
      inkscape:groupmode="layer"
      id="layer3"
+     class="detail-remove"
      inkscape:label="Layer 3"
      style="display:inline">
     <g
@@ -157,4 +158,4 @@
          style="fill:none;stroke:#609926;stroke-width:2.68000007;stroke-linecap:butt;stroke-linejoin:miter;stroke-miterlimit:4;stroke-dasharray:none;stroke-opacity:1" />
     </g>
   </g>
-</svg>
+</svg>