When an agent mute/unmute the converstion, add an activity message "#{agent_name} has muted the conversation"

Problem
The pathname field on the widget_settings table is sometimes longer than the max character limit for DB fields of type "string".

Solution
Migrate the pathname fields on the widget_settings table from type "string" to type "text":

https://github.com/papercups-io/papercups/blob/master/lib/chat_api/widget_settings/widget_setting.ex#L18

**Questions, or need help gett

Where
https://github.com/livechat/livechat-public-docs/tree/master/js-api

Todo

• restructure the _methods.md and _callbacks.md sections, so the menu is more readable,
• suggest using Visitor SDK for advanced usage