Use APP_NAME on home page (#5048)

Would it make sense to actually use the configured app name on the home page?

templates/home.tmpl

@@ -7,7 +7,7 @@
 			</div>
 			<div class="hero">
 				<h1 class="ui icon header title">
-					Gitea - Git with a cup of tea
+					{{.i18n.Tr "app_name"}}
 				</h1>
 				<h2>{{.i18n.Tr "app_desc"}}</h2>
 			</div>