Dialog management cleanup

Summary:
This diff moves the dialogs

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To use the imperative dialog APIs, rather then organising them through reducers which adds a lot of indirection which isn't really needed but hard to follow.

Reviewed By: passy

Differential Revision: D30192002

fbshipit-source-id: ba38b2e700da3e442653786448fcbf85074981ad

desktop/app/src/chrome/ExportDataPluginSheet.tsx

@@ -47,7 +47,6 @@ type DispatchFromProps = {
 type Props = OwnProps & StateFromProps & DispatchFromProps;
 
 const Container = styled(FlexColumn)({
-  width: 700,
   maxHeight: 700,
   padding: 8,
 });