WebUI: Use websockets instead of http polling/API

[kripton]

Currently the Web UI uses HTTP call to the device's API to get/update information like device status, buffer content (Console page), log entries, wireless status counters. Usually, a one second update polling interval is being used which makes the Console seem laggy when the values update often or fade. Websockets provide a nice way to make the Web UI more responsive and faster. Some "live audio mixers" that can be controlled via web browser from a tablet or similar uss websockets for control and signal level display (Soundcraft's Ui series). The client/browser part should not be a problem (and a fallback to polling could be done if the user-agent doesn't support websockets). On the server side (lwIP stack and its http server) impementation will be quite some effort.