Fix show method for DEC symbolics

[jpfairbanks]

@GeorgeR227, notes from today's meeting

[GeorgeR227]

I tried to add a type to the args argument in our show_call to avoid piracy but I can't since the sorted_arguments used in the show_term returns as a Vector{Any}. In that case I'll probably just take the test code as given and just put it in source.