support for active only plugins

if inactive timeout is set to 0 (or not configured) liftie will not try
to fetch the plugin unless the resort is marked as active (iwo: unless
its meta.counter > 0)
add weather plugin using wunderground API

we ask for weather forecast using resort location and then simplify the
response saving only the forecast for the closest period

only enabled if valid wunderground API key is configured and passed as
`WUND_API_KEY` environment variable
add limiter to prevent overuse of weather APIs