Update examples to use nameof(Class.FieldName)

[jzabroski]

Update examples to use nameof(Class.FieldName) instead of hard-coded strings:

See my code review here:
d68c344#r30912841

Fix:

report.DataFields[nameof(Product.Price)].DataFormatString = "{0:c}";
report.DataFields[nameof(LastPurchase)].DataFormatString = "{0:d}";