Proper binding work for the "select" element when "option" list changed

[stalkerg]

Currently, Svelte didn't update value binding if you change options list in select. It's happening because browser didn't fire any event for that case but change value and ui.
A small example here: https://svelte.technology/repl?version=2.13.4&gist=2f292a1414939dfc3f69fccb37b72f73

Also some description of how it works for Angular users:
https://medium.com/@kastepanyan24/how-to-set-selected-option-dynamically-in-angular-6-85c99958cca5

Unfortunately, we should emit an event manually every time when we change the options list.
But I think it's a bad idea because of default behavior very odd, the browser just shifted value instead try to keep current.
If we want to keep current value after DOM modification we should do something like keyd "each" construction.

[antony]

Closing this in favour of #1764 which has more conversation around the issue.