🏷 Added support for labels in WebMail.Online

Labels are simple tags that can be added to messages to organize a more convenient process of working with them. For example, you can divide messages into categories, visually highlight them in the list (color, icon), set their own priorities (Low, Normal, High), statuses (TODO, DOING, DONE, LATER, NOW, WAITING) etc. Labels are also convenient to use for quick filtering of messages and their search.

Detailed information about labels is available in our wiki.