Check for empty values as well as missing values for better performance in the Views exposed widgets.

#969586 Completely refactor the form processing so previews work in overlay. Did a bunch of cleanup in the process, other things may have broken, this will need some shaking out.

#929494, Got an ISO date with select widget working correctly with proper timezone conversions after implementing new FAPI workflow. Now need to get other field types working and add tests.