VirtualDOM related issues / todos

[MartinKavik]

• [x] Event listener patching - https://github.com/seed-rs/seed/issues/138#issuecomment-554961733
• [x] Refs - https://github.com/seed-rs/seed/issues/115#issuecomment-557036133
• [ ] VirtualNode - https://github.com/seed-rs/seed/issues/180#issue-465733737
• [x] Clone elements with listener - https://github.com/seed-rs/seed/issues/316
• [x] Try to remove Ms: Clone restriction.
• [x] Keys - https://github.com/seed-rs/seed/issues/354
• [ ] Lazy - https://guide.elm-lang.org/optimization/lazy.html ?