change logo to Denkmal.org

To unify our corporate identity we should change the logo to "Denkmal.org"
- [ ] Update favicons
- [ ] navigation bar
- [ ] splash screens ios
- [ ] splash screen android app
- [ ] Remove "calendar" icon?
- [ ] Update CM 1.62.7...1.73.0

@christopheschwyzer could you do it on occasion?