User experience is very poor when cquery server startup-crashes #60

When the cquery server startup-crashes (for whatever reason), the user experience is as follows:

• A small line of pixels flickers near the bottom right corner of the window.
• CPU utilization is 100%.

If you click on the small ine of flickering pixels, it briefly resolves into a dialog which reads:

cquery has crashed; it has been restarted.

which stays on screen for a split second, and then disappears again, and there are just flickering pixels again.

If you open the Output window, you sometimes see output related to the crash in the "cquery" section, and sometimes it's just blank.

This is a really poor user experience. A more reasonable user experience would be:

• The extension tries to launch the server once.
• If it crashes on startup, it shows a dialog saying why (e.g. whatever output or logs the server produced), and asks the user to restart the extension or stop trying.