Adding support for DHT11, DHT22 and AM2302

[theyosh]

Requested in #1 for support for other temperature and humidity sensors and power relay switches

This issue will address the sensor request only. The switch request will be fixed in a different issue #3.

This requires a different approach for adding sensors. GPIO sensors are not scanable during startup. So the interface will get an 'add' button to add new sensors. Also there will be a new extra setting which is the 'bus' on which the sensor is. That will be for now: 1wire and gpio

For adding 1 sensor, you have to make two actions in the web interface. Every sensor is either temperature of humidity. So this has to be specified per sensor. And when a GPIO or 1Wire sensor does both it needs to be entered twice