Add class to page content to unify top margin (#13766)

* Add class to page content to unify top margin

Previously pages would individually set this margin but some didn't so
content would stick to the header without any space. Resolve this by
adding a new class that is added on all pages. The only place where we
remove this margin again is on the pages with menu or wrapper in the
header.

* fix admin notices

* fix team pages

* fix loading segment on gitgraph for arc-green

* fix last missing case

Co-authored-by: techknowlogick <techknowlogick@gitea.io>

templates/repo/wiki/new.tmpl

@@ -1,5 +1,5 @@
 {{template "base/head" .}}
-<div class="repository wiki new">
+<div class="page-content repository wiki new">
 	{{template "repo/header" .}}
 	<div class="ui container">
 		{{template "base/alert" .}}

templates/repo/wiki/pages.tmpl

@@ -1,5 +1,5 @@
 {{template "base/head" .}}
-<div class="repository wiki pages">
+<div class="page-content repository wiki pages">
 	{{template "repo/header" .}}
 	<div class="ui container">
 		<h2 class="ui header df ac sb">

templates/repo/wiki/revision.tmpl

@@ -1,5 +1,5 @@
 {{template "base/head" .}}
-<div class="repository wiki revisions">
+<div class="page-content repository wiki revisions">
 	{{template "repo/header" .}}
 	{{ $title := .title}}
 	<div class="ui container">

templates/repo/wiki/start.tmpl

@@ -1,5 +1,5 @@
 {{template "base/head" .}}
-<div class="repository wiki start">
+<div class="page-content repository wiki start">
 	{{template "repo/header" .}}
 	<div class="ui container">
 		<div class="ui center segment">

templates/repo/wiki/view.tmpl

@@ -1,5 +1,5 @@
 {{template "base/head" .}}
-<div class="repository wiki view">
+<div class="page-content repository wiki view">
 	{{template "repo/header" .}}
 	{{ $title := .title}}
 	<div class="ui container">