better namespacing

[petervaro]

• kb_rpi2_Pin(Id|Role|Pull|State)? should be kb_Pin(Id|Role|Pull|State)?, as these objects are generic enough to abstract any SBC's GPIO;
• kb_rpi2_Sensor shoul be be kb_Sensor, as Sensor is not RPi specific;
• kb_rpi2_sensors_X should be kb_sensors_X non of them is RPi specific;