This uses the existing ForkedProjectLinks

When no fork network exists for the source projects, we create a new
one with the correct source

The fork network will keep track of the root project as long as it's
present.

This migration can take a bit of time to complete and I don't want to
delay the deployment process.

Additionally we're delegating missing method calls on GpgKeySubkey to
GpgKey since most of the info required when verifying a signature is
found on GpgKey which is the parent of GpgKeySubkey

Conflicts:
	db/schema.rb