Get the properties of the setup WiFi AP

[jdede]

This PR introduces three new functions for easier handling of the setup WiFi network:

• bool isSetupModeWifiEncrypted(): Returns true if the WiFi is encrypted
• String getSetupModeWifiName(): Returns the SSID of the setup WiFi (ESP32_)
• String getSetupModeWifiSecret(): Returns the secret of the setupt WiFi

This PR is required to fix https://github.com/jamct/DoorsignEPD/issues/19

[jdede]

Good idea @Dirk007 ! Fixed in 8422ad56f1323e3a6682af62a56c30b75d46a092