fix: Update connection status on disconnect

[bmingles]

• Connection status wasn't updating on disconnect editor / server (I added comments to the 2 new lines that fixed this)
• Moved connection related commands + handlers to ConnectionController. This should be the rest of the code. Just moving existing functionality.

Testing

• Run a script against a server to create connection + associate editor
• Status bar item should update to show the server the active editor is connected to
• In the "CONNECTIONS" panel, click the split plug icon beside the editor node to "Disconnect Editor"
• Status bar item should update to "Deephaven: Disconnected"
• Repeat but instead of "Disconnect Editor", click the "Disconnect from Server" icon in the "SERVERS" panel (the split plug beside the server node)

[github-actions[bot]]

End-to-end Test Summary

Tests 📝	Passed ✅	Failed ❌	Skipped ⏭️	Pending ⏳	Other ❓	Flaky 🍂	Duration ⏱️
6	6	0	0	0	0	0	04:57:42

A ctrf plugin

Detailed Test Results

Name	Status	ms	Flaky 🍂
should default to the correct settings	passed ✅	1912
should return custom settings: Empty configs	passed ✅	303
should return custom settings: Populated configs	passed ✅	129
should be able to load VSCode	passed ✅	875
should only be visible when a supported file type is active: test.groovy	passed ✅	2770
should only be visible when a supported file type is active: test.py	passed ✅	958

A ctrf plugin

Failed Test Summary

No failed tests ✨

Flaky Test Summary

No flaky tests detected. ✨