Jobs: Support for job-hold-until/Hold-Job/Release-Job and job-password

[michaelrsweet]

Would be nice to support held jobs and the job-password attribute. Tasks:

• [ ] Support job-hold-until/-time Job Template attribute and associated Printer attributes
• [ ] Support Hold-Job and Release-Job operations
• [ ] Support Hold-New-Jobs and Release-Held-New-Jobs operations (admin)
• [ ] Support job-password/-encryption operation attribute and associated Printer attributes
• [ ] Add Release Job button to web interface (with UI for providing password as needed)