Replace footer and modal icons with SVG (#13245)

- Replace two font icons with SVG in the footer
- Replace icons in delete modals with SVG
- Horizontally center message text in modals

templates/repo/issue/labels/edit_delete_label.tmpl

@@ -1,6 +1,6 @@
 <div class="ui small basic delete modal">
 	<div class="ui icon header">
-		<i class="trash icon"></i>
+		{{svg "octicon-trashcan"}}
 		{{.i18n.Tr "repo.issues.label_deletion"}}
 	</div>
 	<div class="content">

templates/repo/issue/milestones.tmpl

@@ -95,7 +95,7 @@
 {{if or .CanWriteIssues .CanWritePulls}}
 	<div class="ui small basic delete modal">
 		<div class="ui icon header">
-			<i class="trash icon"></i>
+			{{svg "octicon-trashcan"}}
 			{{.i18n.Tr "repo.milestones.deletion"}}
 		</div>
 		<div class="content">

templates/repo/issue/view_content.tmpl

@@ -219,7 +219,7 @@
 
 <div class="ui small basic delete modal">
 	<div class="ui icon header">
-		<i class="trash icon"></i>
+		{{svg "octicon-trashcan"}}
 		{{.i18n.Tr "repo.branch.delete" .HeadTarget }}
 	</div>
 	<div class="content">

templates/repo/issue/view_content/sidebar.tmpl

@@ -611,7 +611,7 @@
 
 	<div class="ui basic modal remove-dependency">
 		<div class="ui icon header">
-			<i class="trash icon"></i>
+			{{svg "octicon-trashcan"}}
 			{{.i18n.Tr "repo.issues.dependency.remove_header"}}
 		</div>
 		<div class="content">