Migrate from bintray to github releases

[infeo]

Due to announced shutdown of brintray, there is the need of moving our CI publishing from to another host.

Github offers with Github releases a convinient way of doing so, especially since this repository already uses Github CI.

Before flipping the switch there are some preperations needed:

• [x] Update the AppImage zsync link
• [x] Release and push a last version of the AppImage to Bintray with the changed update link included

[infeo]

Some tests revealed, that the current bintray update information is already incorrect, i.e. users would not be notified, even if we publish a new release to bintray.

Using the appimage update tool to show update info

user@os:~/Downloads$ ./appimageupdatetool-x86_64.AppImage -d ./cryptomator-1.5.11-x86_64.AppImage 

Parsing file: ./cryptomator-1.5.11-x86_64.AppImage
AppImage type: 2
Raw update information: bintray-zsync|cryptomator|cryptomator|cryptomator-linux|cryptomator-_latestVersion-x86_64.AppImage.zsync
Update information type: ZSync via Bintray
Assembled ZSync URL: https://dl.bintray.com/cryptomator/cryptomator/cryptomator-1.5.12-x86_64.AppImage.zsync

and checking for updates

user@os:~/Downloads$ ./appimageupdatetool-x86_64.AppImage -j ./cryptomator-1.5.11-x86_64.AppImage 
zsync2: 
zsync2: Reading and/or parsing .zsync file failed!
Error checking for changes!

results in an error.

It is caused by a long-ago change, that releases are published under their own library, meaning the correct url would be https://dl.bintray.com/cryptomator/cryptomator/1.5.12/cryptomator-1.5.12-x86_64.AppImage.zsync.

If we make a last release to bintray, we should consider to change the release path manually.

[overheadhunter]

Any objections against re-releasing 1.5.12 app image?

[infeo]

No objections. But the issue should be closed, after all tasks are finished. And the release to gh and bintray is one of the tasks.

[overheadhunter]

Done. Now copying updated appimage to cryptomator/cryptomator releases.