Gracefully handle temporary network disconnects on the guest's side and try to automatically reconnect

[Chuxel]

Product and Version [VS/VSCode]: VS Code 1.20.0-insiders, VS 2017 Preview (15.6 Preview 3)
OS Version [macOS/Windows]: macOS High Sierra, Windows 10 Enterprise 64-bit
Live Share Extension Version: 0.2.58
Target Platform or Language [e.g. Node.js]: Any

Steps to Reproduce / Scenario:

1. [Host] Share a project
2. [Guest] Join
3. [Guest] Quickly turn your network connection off then on again

Expected: The guest is notified of a temporary disconnect, Live Share tries to reconnect (and edits are disabled), and after turning the network connection back on you are reconnected
Actual: The guest is immediately kicked out of the collaboration session and has to rejoin.

This is a feature-level change to resolve.

[Chuxel]

Merging in 271 from @marko1777 . Logs indicate a temporary disconnect that Live Share did not recover from.

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if we both pinned following live share disconnected and after that we got an error that either of us are offline, but we weren't. After my friend restarted VSCODE it has started to work again (My friend was on Ubuntu 17.1 and me on Windows 10)

[jasongin]

Reconnection was implemented last year, but we forgot to close this issue then, so I'm closing it now.

The experience should be that upon disconnection, you'll see a message (gold bar in VS, progress notification in VS Code) indicating that Live Share is attempting to reconnect. If a connection can be re-established in under 60 seconds, then the session should be able to proceed with no loss of data. Otherwise, after reconnect attempts have failed for 60s then the session will end.

If this is not working as expected for anyone, please comment here or open a new issue.