Reverse Sync Symbol for updating the selected symbol

I prefer to have a separate page with all the interface elements that I have build. And a blank new page for the current interface where I use them. Syncing symbols from another page is annoying as you have to navigate to that page, find the correct symbol, hit cmd-e and navigate back to where you were.

What if instead you could hit cmd-alt-e and let Sketch find the first symbol with the same name and update the one you are working with automatically?

Well, this pull request does just that. It's a bit ugly and repeats the code (as there is no library file to use as of yet). But it gets the job done and shows the idea nicely.

What do you think?