It was spot-the-difference time as identical twins Mairi and Amy Johnson (aged 33) helped launch Taylors Snacks, the new brand that is replacing Mackie’s of Scotland crisps and popcorn.  At the Taylors family farm in Errol, Perthshire, the twin sisters from Currie on the outskirts of Edinburgh helped share the message that while the Taylors branding and packaging…