GT for VS Code stops working after the connected workspace is closed

[fregante]

Extensions are run once per workspace, so if there are two workspaces open, GhostText will open the port in one and then fail in the other one.

If the first workspace is closed, the other one does not attempt to open the port again.

Tasks:

• Add enable/disable server commands, so that the user can try to restart the server
• Detect workspace closures and try to reopen the server
• Potentially look into launching a persistent child process and orchestrate VS Code from there, bypassing this setup (this would involve additional message passing step, so it's a last resort)

This also causes:

• VS Code does not focus on the right editor #274