BLVIII-28: Test 2 D plotter view
Add setRate() and getRate() to adjust the rate at which the 2D plot 
is updating, by default is 1.2 s.
Merge branch 'gda-8.40' of ssh://dascgitolite@dasc-git.diamond.ac.uk/gda/gda-core.git into gda-8.40