Handle "merge conflicts" more gracefully when saving sketches

[kyldvs]

Right now if I have the same sketch open in two tabs then do:

1. (tab 1): Write "foo", then save
2. (tab 2): Write "bar", then save
3. (refresh either tab): Observe that only "bar" appears, and "foo" has been lost

There is no confirmation that "bar" is overriding "foo" on the second save. If my initial state of the sketch when I loaded the page is not the same as the current state of the sketch on the server when saving my changes a warning should come up asking me to confirm that I want to save.

[thangngoc89]

I'll look into this. In the mean time, did you lost any content? I can recover it for you

[kyldvs]

Nope no content loss luckily :)