Add app.dht_gpio flag to find DHT sensors

Parse this comma separated string to find GPIO pins on which we must
enable DHT sensors.  Seperators are space and comma.
Can be empty, single GPIO pins, or a list:
app.dht_gpio=""
app.dht_gpio="5"
app.dht_gpio="5,4,14"
app.dht_gpio="5 4 14"
app.dht_gpio="5, 4 14"

mos.yml

@@ -42,6 +42,7 @@ config_schema:
   - ["app.hostname", "sonoff-sv"]
   - ["app.config", "s", {title: "Application specific config file"}]
   - ["app.config", "sonoff-basic.json"]
+  - ["app.dht_gpio", "s", "5,4,14", {title: "Comma Separated list of GPIO pins to enable DHT22/AM2302 sensors on"}]
 
 
 #build_vars: