Add welle.io app

Required

• The app complies with the inclusion criteria
• The original app author has been notified (and does not oppose the inclusion)
• All related fdroiddata and RFP issues have been referenced in this merge request
• Builds with fdroid build

Strongly Recommended

• The upstream app source code repo contains the app metadata (summary/description/images/changelog/etc) in a Fastlane or Triple-T folder structure
• Releases are tagged

Suggested

• External repos are added as git submodules instead of srclibs
• Enable Reproducible Builds
• Multiple apks for native code

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welle.io uses

• Qt for android 5.15 for versions 2.3 & 2.4
• Qt for android 6.4 for development version