Update Chum Metadata to new format

[nephros]

while on the topic of updating things for chum, lets use the newer metadata format.

[jmlich]

It looks good to me. It matches fields described at https://github.com/sailfishos-chum/main/blob/main/Metadata.md

Donation field can be probably added into Links section.

  Donation: https://www.paypal.me/piggz