IP fxns for ESP8266

- fixed int/uint warning
- added functions to get local IP address with esp8266
- fixed local ip fxn for xbee
- removed extra test builds
- set travis to build all modems in tests

tools/test_build/test_build.ino

@@ -4,12 +4,6 @@
  *
  **************************************************************/
 
- // #define TINY_GSM_MODEM_SIM800
- #define TINY_GSM_MODEM_A6
- // #define TINY_GSM_MODEM_M590
- // #define TINY_GSM_MODEM_ESP8266
- // #define TINY_GSM_MODEM_XBEE
-
 #include <TinyGsmClient.h>
 
 TinyGsm modem(Serial);