chore: adapt theme to new template system (#696)

* Adapted theme's layout to [Hugo v0.146.0](https://gohugo.io/templates/new-templatesystem-overview/)
* Bumped minimal Hugo version to v0.146.0

layouts/_partials/utils/icon.html

@@ -0,0 +1,14 @@
+{{/* Render raw svg icon from .Site.Data */}}
+{{- $icon := index site.Data.icons .name -}}
+
+{{- if not $icon -}}
+  {{ errorf "icon %q not found" .name }}
+{{- end -}}
+
+{{- $icon = $icon | safeHTML -}}
+
+{{- if .attributes -}}
+  {{- $icon = replaceRE "<svg" (printf "<svg %s" .attributes) $icon -}}
+{{- end -}}
+
+{{- return ($icon | safeHTML) -}}