Inverted position shifting idle logo (#1484)

* Inverted idle logo

Back on white background start-up logo.
Inverted idle logo with random positioning.

* Idle Logo display default true

DISPLAY_IDLE_LOGO true as burn-in screens saver, especially fo the constant heading and line

* Display Brightness added

* SSD1306toMQTT / MQTTtoSSD1306

Additional "onstate" and "brightness" setting and regular display state reporting

Docs - separate Displays section

docs/.vuepress/config.js

@@ -88,6 +88,7 @@ module.exports = {
             'use/sensors',
             'use/actuators',
             'use/boards',
+            'use/displays',
             'use/gateway'
           ]
         },