Make command async, improve output buffer behavior

[liggitt]

Sorry for the mega pull, feel free to pick just the commits you want

• Async launching to avoid blocking
• Keep previous results in output screen (like default find behavior)
• Clean up output view (mark as scratch, hide line numbers)
• Make quick panel monospace
• Add syntax highlighting to output results to show line numbers
  • matches xml, json, and plain output formats
• Add double-click jump-to support
  • fires on selection change of a line containing a reference
  • matches xml, json, and plain output formats