TOMO-21 Write Metadata to Nexus.

Initial code
TOMO-24 Metadata from NXMetaDataProvider now handled by NexusDataWriter

NXMetaDataProvider is a zero input/extra scannable which at scan Start 
generates the neux tree to be written
TOMO-24 Handle extra and input fields in scannables
GDA - Add dependency on math3 for Pair type
TOMO-24 NXMetaDataProvider
TOMO-24 Remove unrequired classes written during development of this
feature
GDA-5553 allow for normal behaviour of welcome screens

i.e. have one on the first startup only.  If you wish to hide/show your
welcome screen then set the gda.gui.window.force.intro java property
accordingly.
Merge branch '8.30' of ssh://dasc-git.diamond.ac.uk/gda/gda-core into 8.30