ADVIEWER (8.40) Replace all occurences of MPeg with MJPeg.

MJPegView.Id really should be corrected from "uk.ac.gda.epics.adviewer.mpegview"
to "uk.ac.gda.epics.adviewer.mjpegview" since Mpeg and Mjpeg are different
and we may want to implement mpeg streams in the future.
Merge branch 'gda-8.40' of ssh://dascgitolite@dasc-git.diamond.ac.uk/gda/gda-epics.git into gda-8.40
Merge branch 'gda-8.40' of ssh://dascgitolite@dasc-git.diamond.ac.uk/gda/gda-epics.git into gda-8.40