Implement modem (attempt 2)

[ed7coyne]

Killed the last PR (#66) when I tried to rebase it. abandoning and copying all content to this one.

[proppy]

I think we forgot to update the examples:

FirebasePush_ESP8266:24: error: use of deleted function 'Firebase::Firebase(const Firebase&)'
                    .auth("secret_or_token");
                                           ^
In file included from /home/proppy/Arduino/libraries/firebase-arduino/examples/FirebasePush_ESP8266/FirebasePush_ESP8266.ino:20:0:
/home/proppy/Arduino/libraries/firebase-arduino/src/Firebase.h:44:3: error: declared here
   Firebase(const Firebase&) = delete;
   ^
/home/proppy/Arduino/libraries/firebase-arduino/examples/FirebasePush_ESP8266/FirebasePush_ESP8266.ino: In function 'void setup()':
FirebasePush_ESP8266:29: error: 'WiFi' was not declared in this scope
   WiFi.begin("SSID", "PASSWORD");
   ^
FirebasePush_ESP8266:31: error: 'WL_CONNECTED' was not declared in this scope
   while (WiFi.status() != WL_CONNECTED) {
                           ^
exit status 1
use of deleted function 'Firebase::Firebase(const Firebase&)'

[proppy]

Reverting so that it's not broken over the week end, we can re-revert on monday after we fix it.