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/view_content/sidebar.tmpl

@@ -1,4 +1,4 @@
-<div class="issue-content-right ui segment">
+<div class="issue-content-right ui segment" data-global-init="initRepoIssueSidebar">
 	{{template "repo/issue/branch_selector_field" $}}{{/* TODO: RemoveIssueRef: template "repo/issue/branch_selector_field" $*/}}
 
 	{{if .Issue.IsPull}}

templates/repo/issue/view_content/watching.tmpl

@@ -2,10 +2,10 @@
 	<input type="hidden" name="watch" value="{{if $.IssueWatch.IsWatching}}0{{else}}1{{end}}">
 	<button class="fluid ui button">
 		{{if $.IssueWatch.IsWatching}}
-			{{svg "octicon-mute" 16 "tw-mr-2"}}
+			{{svg "octicon-mute" 16}}
 			{{ctx.Locale.Tr "repo.issues.unsubscribe"}}
 		{{else}}
-			{{svg "octicon-unmute" 16 "tw-mr-2"}}
+			{{svg "octicon-unmute" 16}}
 			{{ctx.Locale.Tr "repo.issues.subscribe"}}
 		{{end}}
 	</button>