AreaDetector - use Observable<Short> to monitor state of enum
EPICS - Add support for WriteMessage, WriteStatus in NDFile
EPICS - ADBase acquireState is an enum, not a String
EPICS - FileWriterBase supports WriteStatus PV
EPICS - throw DeviceException if FFilePathExists PV indicates error
EPICS - Move checking for file existence into the read method as this
runs on the scandatapoint pipeline
GDA EPICS - Class to hold data extracted from NDArray plugin in form to
add to NXDetectorData
GDA Core - Implement callReadBeforeNextExposure and
requiresCacheBackedPlugins

Use new ArrayData class
EPICS - handle changed in method names  to supportsAsynchronousRead and
requiresAsynchronousPlugins
EPICS - Add paragraph breaks to comment
EPICS - Simplify constructor for NXDetectorDataArrayAppender
EPICS - Add observer of WriteStatus PV
EPICS - Add waitUntilFileExists property to SimgleImageperFileWriter
EPICS - Handle change in hierarchy of NXPlugins
EPICS - FileWriterBase - Ensure writeStatus updates are observed. Add
clearWriteStatusErr method
Merge remote-tracking branch 'origin/8.34'