Release 4.1.0

• t-u: Add a setup-kdump command; implements [jsc#PED-1441]
• Add support for ULP (Userspace Live Patching) [jsc#PED-1078]:
  • Export TRANSACTIONAL_UPDATE_ROOT (the path to the snapshot) in the update environment
  • Unfortunately requires a separate bind mount in /tmp again for the update environment, as libpulp has to be able to access the snapshot directly, without it being bind mounted on itself
• Add support for "notify" reboot method for desktop use [gh##93]
• Fix kdump initrd recreation detection; the check was performed in the active snapshot instead of the target snapshot
• Document register command [bsc#1202900]
• Avoid unnecessary snapshots for register command [bsc#1202901]
• Various optimizations for register command
• Remove bogus error message when triggering reboot
• Rework /etc overlay documentation in "The Transactional Update Guide"
• Fix incorrect manpage formatting
• Remove leftover "salt" reboot method in configuration example file
• Replace deprecated std::mem_fn with lambdas