Handle missing weather symbols in data

[vegardb]

If a weather symbol for some reason is missing from the data, defaults vary a bit:

• Hourly and daily data just shows the fair_day symbol
• Today's forecast shows the text 'Not available'

We should find the best way to handle this.

Maybe @LinUXBele or @SairanW have some opinions on this?

[vegardb]

Same applies to all other values