preset enhancements and chores

[FN-FAL113]

Changes

• when creating a preset you need to double click check boxes to select; only one click should be needed
• button to invert selection
• button to block all servers except the ones in a preset
• intentionally Disallow preset multi-select
• change delete preset form to a confirmation instead of typing preset name
• allow to edit preset

Issues

• Resolves #47 (thanks for the great suggestions)