Web: edit status changed flash message

Now says "... status has been changed to .." because "... status has
been updated to ..." doesn't make sense.
Web: add SAMP broadcast buttons for FITS outputs

Currently assume that any FITS output file is an image and
show a button allowing the SAMP mtype image.load.fits to be
broadcast.  The broadcasting code is based on the sampjs
example file "broadcaster.js".  sampjs itself has not been
added to the repository as its license is unclear.