Add support for default values of optional analysis parameters

Idea:

Function/WAVE MyAnalysisFunction_GetDefault(string name)
                                                              
    strswitch(name)
        case "optParam1":
             return {1, 2, 3}
             break
       case "optParam2":
             // no good default
             return $""
             break
        default:
             ASSERT(0, "Unimplemented for parameter " + name)
             break
    endswitch
End

XXX_GetDefault:

• must only handle optional parameters
• can pack strings/numbers into single element (text) waves
• only text waves and FP/DP waves are accepted as returned waves
• can return $"" for saying "want to handle that at runtime" or "no good default"
• Don't allow stimset saving (interactively from WB GUI) and DAQ starting if the default values don't pass the XXX_CheckParam tests or the function does not adhere to the requirements here.

Tasks:

• Implementation including AFH_ helper function
• Suggest default value in wavebuilder GUI
• Tests

Start by tracing the proposed XXX_GetDefault and AFH_ helper responsibilities, then inspect how XXX_CheckParam validation, stimset saving, DAQ starting, and the WaveBuilder GUI currently handle optional parameters. The work is done when implementation, GUI default suggestions, and tests cover the listed requirements and invalid defaults are rejected.