GPIO viewer in Berry initial version using async webserver

[s-hadinger]

Description:

Initial version for GPIO Viewer back-end in Berry. This is leveraging the newest Async Webserver in Berry.

Paste tasmota.urlbecload("http://ota.tasmota.com/tapp/gpioviewer.bec") in the Berry console

Connect to http://<your_tasmota_ip:5555/

Checklist:

• The pull request is done against the latest development branch
• Only relevant files were touched
• Only one feature/fix was added per PR and the code change compiles without warnings
• The code change is tested and works with Tasmota core ESP8266 V.2.7.4.9
• The code change is tested and works with Tasmota core ESP32 V.2.0.14
• I accept the CLA.

NOTE: The code change must pass CI tests. Your PR cannot be merged unless tests pass