Implementing open/close button

[donatmarko]

This pull request implements the possibility to connect a button to the microcontroller as an open/close button.
It is useful when the device is connected to a latching electromagnetic lock in which case the lock can't be circumvented - the magnet must be disabled to open the door - when someone wants to leave the room.

I can imagine another scenario for the usage of this button:
Given an office where we usually have lots of guests and this room is protected by ESP RFID.
To avoid walking to the door and opening it manually every time when someone knocks (without having RFID tag), we may place one or even more buttons near our workplaces to allow us to let the guests in without the need to walk to the door.

It utilizes the Bounce2 (https://github.com/thomasfredericks/Bounce2) library to properly debounce the button. The input is configured to use the internal pull-up resistor, therefore we consider the low state of the button as pressed.

Every time the button is pressed, a log entry is being created in the Access Log.

[omersiar]

Nicely done. I am reviewing it right now.