Replace SNR with S/N

As recommended by Frossie to avoid confusion with supernova
remnants.  Tried to remove SNR from the words.txt file but
had to add a bunch of extra words which the version of aspell
I'm using just now doesn't know.  At first I thought removing
SNR without re-ordering the list however aspell does it was
corrupting it somehow.
Refer to the new labels on the "histogram"

The first peak blends together daisy, pong-900 and pong-1800.
But I didn't want to add too much information here because it's
in the next section where I explain what "pong" and "daisy" mean.
Add summary of range of targets

Added the list of target types suggested by Frossie to the
introduction.
Prevent lists splitting from their intro. lines
Remove unnecessary of
Remove trailing comma from Shepherd URL
Adjust \cite command placements

Now before the acronyms, to match the style used by
TJ for JSA in the introduction.  Also moved the one for
HARP commissioning to make it clearer that it refers
to the result of interest.
Perform spellcheck
Adjust centering of the publications chart
Commit re-generated "histogram" (with labels)