Prompt upon trying to close the tab with an unsaved content

[ivanbatic]

When user changes the content of the file, does not save it, and tries to close the tab, we should prompt them and make them confirm the loss of data.

[mayacoda]

Actually, the user should be able to close an edited tab without being prompted, because a local copy of the document should be cached regardless. The prompt should only occur when the user tries to close the application (browser tab).

[mayacoda]

Prompt should be when user is leaving the editor (so closing browser tab or window)