use append/3 after discussion with Paulo and Jan

append/3 is part of the Prolog Prologue and has the following
additional didactic advantage: It shows how we can easily obtain more
general versions of next/3, and see what happens for example if we
interpret "near" as "up to two places away" by adding clauses like:

   next(A, B, Ls) :- append(_, [A,_,B|_], Ls).
add zebra_owner/1 and water_drinker/1, remove setof/3 examples as suggested by Jan
Get rid of # URLs because they do not refresh properly and interact with
the modal dialogues
Removed loadHashSource()
Make examples simply move to the target URL
Allow example directories without index.json
Describe storage options.
Trying to make a sensible history.
MODIFIED: Many changes to storage, getting rid of #URLs
No longer needed dependency
Moved SWISH to the root