LLVM 19 and cmake 20

GIT_SILENT Sync po/docbooks with svn

Keep icons and plasma in the appimage

FindClang.cmake: look also for LLVM 12 & 13

add build icu

Tagging 5.5.2

Tagging 5.5.1

Tagging 5.5.0

Tagging 5.4.80

Tagging 5.4.6