Set version and tag to 5.4.1

Flatpak manifest template: Adding quotes around tag value

Java 21 required even for installed or master branch

MacApplication modified to point to Preferences rather than low-level…

… Constants

Cross-building of flathub content

Use tag 5.4-alpha-3 to build flatpak

Flatpak handover from Windows to Linux 1

Handbook: addition of the Snippet chapter

Merge branch 'development'

Merging development to master