BLVIII-24 make more resilient to errors, prevent ConcurrentMoificationException in JythonServer, remove requirement to define the x and y points before the scan starts
BLVIII-24 prevent ConcurrentMoficationException

This would happen if observers deregister themselves inside thier update() method - which they might want to based on what events were sent.
CORE: Rix ConstantVelocityRasterScans to work on beamlines with concurrent detector readout configured
TwoDScanPlotter was plotting each point of the scan. To improve performance 
for fast scan the plot is updated with a rate of 1.2 s.
It will be upgraded soon to allow the control of the plot rate.
Merge branch 'gda-8.40' of ssh://dascgitolite@dasc-git.diamond.ac.uk/gda/gda-core.git into gda-8.40