Add a function slide

[DominicSmith]

An option that sits alongside the others like full screen image etc. Can be added when building a Mural, but isn't a visible object. Could include functions like 'Jump to X slide' or 'Advance next slide after X seconds' or 'Jump to X (X could be any point in a different Mural to embed Murals within Murals or create 'Hyper Murals')' This would be a big aid in building self running / closed loop Murals for gallery and display situations and could mean you could make a 'Mother Mural' that takes you to a bunch of related Murals.