[UI/UX Enhancement] Button tooltips

[dwughjsd]

In current version, buttons don't have proper tooltips and only show keyboard shortcut of the pressed action.

Current behavior:

Shown in image.

Expected behavior:

Tooltip being "Bold (Ctrl + B)" (localized in Chinese: "加粗（Ctrl + B）").

I don't have sample images for the expected behavior because most phone app doesn't show keyboard shortcuts. It's good to keep them in tablets UI, while it won't be a bad idea to hide them on phone.