Add null/not null filters and fix the date picker#4

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sitharus wants to merge 5 commits intomasterfrom

Commits on Jan 15, 2017

Fix the calendar control.
Phillip Hutchings
committed
Initial support for is null/is not null/not equals
Phillip Hutchings
committed
Add new filters to date/text types
Phillip Hutchings
committed
Refactor number filters to use a common base
Phillip Hutchings
committed
Add new filter types to the UI
Phillip Hutchings
committed