Remove silly public version of getNdfile and change visibility of
sensible version.
NDFile - add waitWhileStatusBusy for use when using CAPTURE mode
Allow Spring config of FileWriteMode - to allow CAPTURE
Allow for detectors with fixed exposure times that run continuously

We need to read the exposureTime from the hardware.
Use ndFile plugin to 'grab' the images to be written to disk.
Do not stop a detector at the end of a scan if it should run
continuously
When running continuously we need to wait for the acquire period before
resetting the summation in the proc plugin.
NDFileHDF5 - add set/get for colChunks, framesChunks and framesFlush
ADDetector - aborting waiting for file if scan is interrupted
Make use of extensions to NDFileHDF5 in FileWriter
Make use of new Camera CAPTURE PV on I12 
Enable PROC callback in collectData to allow skipping of first image
Handle case when IOC crashes and the PutListener never gets called.