Add XML summary comments to fields in Options class

[abgoswam]

We need to add XML summary comments to fields in Options class.

Learners where its missing:

• SdcaBinaryTrainer
• SdcaMultiClassTrainer
• SdcaRegressionTrainer
• StochasticGradientDescentClassificationTrainer
• MulticlassLogisticRegression + related LR learners
• Online learners

Also, in XML help for options we should say something consistent (right now there is inconsistency in the help text for options)
e.g.

/// <param name="options">Advanced **options** to the algorithm.</param>

[wschin]

I think we have finished this during our API season.