Add Hostname to Wifi Connection

[intractve]

Utilize ota_hostname variable from User_config.h to generate hostname for friendlier display on router's connected devices instead of ESP_xxxxxx

Add hostname setting to both Manual and WifiManager setups

[intractve]

The modifications are inside the if statements for ESP8266 or ESP32 only. Not sure why it's affecting Uno etc. in Travis CI

[1technophile]

Hello,

Thanks for this PR, regarding arduino it seems that the hostName variable is already used in some arduino libraries:

OpenMQTTGateway:169: error: 'char hostName [30]' redeclared as different kind of symbol
 char hostName[30] = {0};

Maybe try to change the name of the variable.

For ESP32 it seems that there is no ESP.getChipId()) function available

OpenMQTTGateway:245: error: 'class EspClass' has no member named 'getChipId'
     sprintf(hostName, "%s-%06X", ota_hostname, ESP.getChipId());
                                                    ^
/usr/local/share/arduino/OpenMQTTGateway/OpenMQTTGateway.ino: In function 'void setup_wifi()':
OpenMQTTGateway:385: error: 'class WiFiClass' has no member named 'hostname'
   WiFi.hostname(String(hostName));

[intractve]

Closing this PR to come up with a better more inclusive solution that passes all tests