Remove/replace links pointing to GNOME Calendar, and update branding

The GNOME devs here seem unnecessarily combative/obstinate for an issue that could've been amicably resolved if approached more collaboratively.

They "strongly object to your downstream modifications of our app against our will", the Mint dev asks what modifications, they "can't pinpoint anything besides "everything"", the Mint dev finds there's only one patch and it only affects other DEs, they accuse the Mint dev of "fixating on these "changes"".

The Mint dev explains that removing GNOME Calendar from Mint's repository wouldn't fix the issue because Mint also pulls packages from Debian/Ubuntu's repository which contains the same version, and proposes a short-term fix of Mint patching out the support link. The GNOME dev misses the point and responds "stop with the whataboutism. It doesn't matter to us if Debian's and Linux Mint's package share the same technical problems".

They seem uninterested in a constructive technical conversation/solution ("we have no interest in these intricate details"), just in melodrama/rhetoric ("honestly, shame on you for pushing this onto Debian").