Replace fomantic divider module with our own (#25539)

Should look exactly like before for normal dividers. "Horizontal" ones
look better because they no longer use image backgrounds.

<img width="917" alt="Screenshot 2023-06-27 at 19 07 56"
src="https://github.com/go-gitea/gitea/assets/115237/d97d8dec-6859-44a8-85ba-e4549b4dd9df">

<img width="914" alt="Screenshot 2023-06-27 at 19 05 58"
src="https://github.com/go-gitea/gitea/assets/115237/8bf98544-2d82-4ebf-ac68-d6dc237bd6b2">

<img width="1246" alt="Screenshot 2023-06-27 at 19 00 42"
src="https://github.com/go-gitea/gitea/assets/115237/36a6bb21-6029-4f53-8bee-535f55c66fed">

<img width="344" alt="Screenshot 2023-06-27 at 18 58 15"
src="https://github.com/go-gitea/gitea/assets/115237/a9e70aee-8e6b-4ea1-9e93-19c9f96aec6e">
<img width="823" alt="Screenshot 2023-06-27 at 18 56 22"
src="https://github.com/go-gitea/gitea/assets/115237/e7a497cd-f262-4683-8872-23c3c8cce32f">

<img width="330" alt="Screenshot 2023-06-27 at 19 21 11"
src="https://github.com/go-gitea/gitea/assets/115237/42f24149-a655-4c7e-bd26-8ab52db6446b">

templates/user/auth/activate.tmpl

@@ -38,7 +38,7 @@
 							<p class="center">{{.locale.Tr "auth.manual_activation_only"}}</p>
 						{{else}}
 							<p>{{.locale.Tr "auth.has_unconfirmed_mail" (.SignedUser.Name|Escape) (.SignedUser.Email|Escape) | Str2html}}</p>
-							<div class="ui divider"></div>
+							<div class="divider"></div>
 							<div class="text right">
 								<button class="ui primary button">{{.locale.Tr "auth.resend_mail"}}</button>
 							</div>