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/repo/issue/sidebar/project_list.tmpl

@@ -5,7 +5,7 @@
 <div class="issue-sidebar-combo" data-selection-mode="single" data-update-algo="all"
 		{{if $pageMeta.Issue}}data-update-url="{{$pageMeta.RepoLink}}/issues/projects?issue_ids={{$pageMeta.Issue.ID}}"{{end}}
 >
-	<input class="combo-value" name="project_id" type="hidden" value="{{$data.SelectedProjectID}}">
+	<input class="combo-value" name="project_id" type="hidden" value="{{if and $pageMeta.CanModifyIssueOrPull $data.SelectedProjectIDs}}{{index $data.SelectedProjectIDs 0}}{{end}}">
 	<div class="ui dropdown full-width {{if not $pageMeta.CanModifyIssueOrPull}}disabled{{end}}">
 		<a class="fixed-text muted">
 			<strong>{{ctx.Locale.Tr "repo.issues.new.projects"}}</strong> {{if $pageMeta.CanModifyIssueOrPull}}{{svg "octicon-gear"}}{{end}}