* Renamed MySensor.h -> MySensors.h
Replaced all references to MySensor.h in examples with MySensors.h
* MySensorCore.* renamed to MySensorsCore.*
This should make it comply more with naming standards
* Updated reference to MySensors core lib
In order to build core tests, there cannot be any hard coded
GATEWAY flags (like MY_GATEWAY_ESP8266). These needs to be set
in the sketch that implements the gateway.