Add weather alerts

[leolost2605]

Partly fixes #29

Alerts the user about weather alerts found for their region. Should work (or at least it's advertised to work) worldwide and polls hourly. Uses the free API api.weatherapi.com (https://www.weatherapi.com/).
I have to admit that I'm not really familiar with accessing web API's like this so if I did something wrong I'd be happy to know.
For now to do some testing I used the aforementioned api because it's easy to use, free (at least for a million calls per month which might be limitting and we probably should mention them somewehere) and allows pretty much any use even with the free plan (no legal expert here though). I hardcoded an api token that's associated with a free account i created there (I know probably not very smart :)). I'm really no expert in this so if there are better apis or if there are other problems (also a million calls per month is probably not enough because with a every day use of 5 hour it ends up at around 6000 users, if we limit polling to once daily it would still only be 30000 users) because of this please tell me. It should be pretty easy to switch as long as it's an json api.

Also the UX side probably could need some improvements especially some clearer phrasing or better icons. Maybe we should even add a default action that opens another window with a detailed description or opens a website etc.)

[leolost2605]

The only really viable free option I see so far will eventually be open-meteo as they are planning to implement alerts at open-meteo/open-meteo#351 and don't require an API key. We also could use separate free governement API for US and EU but there is no way we'll ever cover the whole world this way and it starts to get time consuming. We also could ask users to provide their own API keys but that's not very user friendly.

All in all I'd just like to know whether using free API keys is a no go or a valid possibility we should pursue :)