Seahub UI (#5261)

* [top toolbar] fixed the position of the vertical line between 2 sides

- fixed it for all the pages
- removed the duplicated 'div.main-panel' in 'lib-content-view'

* [search] modified the UI

* [top toolbar] redesigned the notification

* [top toolbar] avatar & the triangle: modified the UI

* [left side panel] updated the UI; fixup & improvement

* [misc] modified links' color, op-icon, and etc.

* [misc] updated UI for share dialog, other dialogs, & 'more operations' dropdown

* [misc] UI: modified markdown side panels, comment panels, input/textarea placeholder

* ['user settings' page] modified UI

* [shared dir upload link page] modified the UI

* [user settings] modified the UI

* [user settings] fixup

* [seafile-ui.css] use an updated one (modified color of buttons)

frontend/src/pages/org-admin/index.js

@@ -66,7 +66,7 @@ class Org extends React.Component {
     return (
       <div id="main">
         <SidePanel isSidePanelClosed={isSidePanelClosed} onCloseSidePanel={this.onCloseSidePanel} currentTab={currentTab} tabItemClick={this.tabItemClick}/>
-        <div className="main-panel o-hidden">
+        <div className="main-panel">
           <Router className="reach-router">
             <OrgInfo path={siteRoot + 'org/orgmanage'}/>
             <OrgUsers path={siteRoot + 'org/useradmin'} />