Improve WiFi setup

[mkalkbrenner]

Thanks to @bartdesign, ZeDMD gets a great new WiFi setup process.

As an improvement, ZeDMD should display the SSID and the password and one sentence of explanation on the display if it switches to server mode.

In case of having multiple ZeDMDs, the SSIDs are conflicting. Isuggest to add a random number between 0 and 99 to the SSID.
If we display the SSID, that isn't a problem.

[mkalkbrenner]

Another issue is that multiple ZeDMDs within the same WiFi network are all running MDNS and return zedmd-wifi.local.

Now that we have the new settings menu in place, we could add a device number to it.

Then we could derive the SSID and the MDNS name from it. For example allowing values from 0 to 9:

• 0
  • SSID: ZeDMD-WiFi
  • MDNS: zedmd-wifi.local
• 1
  • SSID: ZeDMD-WiFi-1
  • MDNS: zedmd-wifi-1.local
• 2
  • SSID: ZeDMD-WiFi-2
  • MDNS: zedmd-wifi-2.local
    ...

In case of 0 there's no suffix to keep backward compatibility.

[mkalkbrenner]

But this feature does only make sense if we support multiple devices at once in libzedmd.

[mkalkbrenner]

OK, for the use case to configure multiple ZeDMDa in WiFi mode, it should be sufficient to have different SSIDs.
We now have a four character uinique ID that will be appended to the SSID.