IPP INFRA Proxy Support

[michaelrsweet]

Add support for functioning as an IPP INFRA Proxy, using both the PWG 5100.18 (INFRA) and PWG 5100.22 (SYSTEM) operations to register and accept print jobs via an INFRA server. Specific tasks:

• Proxy threads for synchronizing printer and job state.
• Web interface for adding/removing INFRA servers and doing any necessary authentication.
• API for adding/removing INFRA servers w/auth info
• API for querying INFRA servers
• Adding of INFRA servers to the save/load functions
• Secure storage for auth info

[michaelrsweet]

Stretch goal: consider whether to add support for Microsoft "universal print service" REST APIs as an alternative to the System service Register-Output-Device operation.