dataengines/weather: Add probability of precipitation for more providers

We were just retrieving the probability of precipitation from 2 out of the 5 weather providers we use ('envcan' and 'wetter.com').

'bbcukmet' doesn't provide this data in the rss forecast feed we read.

Parse and provide this information for the two remaining providers ('dwd' and 'noaa')

noaa (US)	dwd (Germany)