DropDownField now includes automatically the empty option.
Simplified public properties in QueryFieldBase to only show the really public ones.
Removed QueryFieldBase.DataField property since with Name is enough.
Added Placeholder super property in GridExtender.
Made GridExtender.AutoFilterDelay respect the value set in the fields (if any)
Improved some code comments.
Merge branch 'master' of github.com:andreschort/query