Add requirements for pool to VT client

[GwnDaan]

To enhance backwards compatibility, object pools should be able to add certain hardware requirements on their pools. If the VT server doesn't comply with any of the pools' requirements, then we should upload a "minimally compatible pool" to let the operator know incompatibility.

Requirements can include:

• VT server version
• minimum/maximum datamask dimensions
• minimum/maximum softkey dimensions
• Specific small/large font sizes or font styles
• Specific supported graphic modes
• Specific hardware features (See D.9 byte 4)
• the WideChars supported
• Window data mask background color of user-layout datamask/softkeymask
• Supported objects

Do we want to check the requirements via a callback, or let the application provide it when registering the pool? Thoughts?