Refactor issue sidebar and fix various problems (#37045)

Fix various legacy problems, including:

* Don't create default column when viewing an empty project
* Fix layouts for Windows
* Fix (partially) #15509
* Fix (partially) #17705

The sidebar refactoring: it is a clear partial-reloading approach,
brings better user experiences, and it makes "Multiple projects" /
"Project column on issue sidebar" feature easy to be added.

---------

Signed-off-by: wxiaoguang <wxiaoguang@gmail.com>

templates/base/head_navbar_icons.tmpl

@@ -5,14 +5,14 @@
 	{{- $notificationUnreadCount := call $data.GetNotificationUnreadCount -}}
 	{{if $activeStopwatch}}
 	<a class="item active-stopwatch {{$itemExtraClass}}" href="{{$activeStopwatch.IssueLink}}" title="{{ctx.Locale.Tr "active_stopwatch"}}" data-seconds="{{$activeStopwatch.Seconds}}">
-		<div class="tw-relative">
+		<div class="tw-relative flex-text-block">
 			{{svg "octicon-stopwatch"}}
 			<span class="header-stopwatch-dot"></span>
 		</div>
 	</a>
 	{{end}}
 	<a class="item {{$itemExtraClass}}" href="{{AppSubUrl}}/notifications" data-tooltip-content="{{ctx.Locale.Tr "notifications"}}">
-		<div class="tw-relative">
+		<div class="tw-relative flex-text-block">
 			{{svg "octicon-bell"}}
 			<span class="notification_count{{if not $notificationUnreadCount}} tw-hidden{{end}}">{{$notificationUnreadCount}}</span>
 		</div>