change logo to Denkmal.org

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