Add support for enabling PWS with local persistence

[ruimarinho]

If a PWS (Personal Weather Station) is configured (currently, only the WU type is recognized by the code), OpenSprinkler-Weather will automatically register the route /weatherstation/updateweatherstation.php to capture the WU data stream.

However, it only saves changes from the captured stream if the WEATHER_PROVIDER is set to local. In my opinion, this is too restrictive, as one might want to collect observations before switching to the local weather provider.

Therefore, I suggest testing for the presence of the PWS variable instead, allowing the capturing system to function fully without requiring a provider switch.

[mellodev]

@rayshobby we should review if this can be closed/integrated when the recent weather related changes are complete cc @Ncp294