Print trivial groups with 0 or >=1 generators differently?

[fingolfin]

This was suggested on issue #1239 by @laurentbartholdi

Right now, trivial groups with zero generators are printed/viewed/displayed just like those with >= 1 generators:

gap> g:=Group(());
Group(())
gap> h:=Group([],());
Group(())
gap> Print(h);
Group( () )
gap> Display(h);
Group( () )

The first suggestion then is to print them differently: The output of Print and PrintString (and possibly also String, Display, DisplayString could/should be so that reading it back into GAP recreates the original group. So the two groups in the examples would be different.

The second suggestion is to have ViewObj and ViewString show both groups as Group().

[fingolfin]

My personal thoughts are that the first suggestion is fine. I am not so keen on the second one: With Group(()) I see at a glance that this is a trivial permutation group (as opposed to a trivial pc group, fp group, etc.:

gap> FreeGroup(0);
<free group on the generators [  ]>
gap> TrivialGroup(IsPcGroup);
<pc group of size 1 with 0 generators>

[fingolfin]

Of course one could also print those trivial permutation groups as <perm group of size 1 with 0 generators> resp. <permutation group of size 1 with 1 generators> etc.

Or, if one wants code that "can be read back into GAP", then perhaps TrivialGroup(IsPermGroup) or Group([], ()); for the zero generator version...