Merge branch 'stable' into devel

Conflicts:
	config/base_branch
	debian/changelog
	wiki/src/upgrade/v2/Tails/4.5.1/amd64/alpha/upgrades.yml
	wiki/src/upgrade/v2/Tails/4.5.1/amd64/stable/upgrades.yml

Ensure our base_branch is devel.

Resolve conflict in changelog by merging the 4.5 entry, dropping the 4.6
stub, and preferring the 4.11 stub.

Add 4.5.1 UDF stubs as they're to be used for the upcoming emergency
release if required.