'Display files' in the file tree panel
* fixup for sdoc: when hover the other menu options in the first-level menu,
hide the sub-menu
* for 'Display files': refactored the memu option and removed the bad effect on the other menus & menu
options
make 'convert to markdown', 'convert to docx', 'export as docx' as its
sub-menu options
- menus: the 'more operation' menu for the current `<tr>`,
the 'more operation' menu for the single selected file,
the context menu
* [icon] replaced 'sf2-icon-caret-down' with the new 'sf3-font-more'
* ['delete' icon] replaced all the 'sf2-icon-delete' icon with the new 'sf3-font-delete1' icon
* [UI] modified the colors of the operation icons in pages
* [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)
