ENHANCE: Two-Cohomology for arbitrary finite groups

Uses rewriting system since pc presentation will not always be available.

TWOCOHOM: Add info from decomp.

ENHANCE: Wreath product order. Permrep.

Use a rewriting system based on extensions for the factor group (as it is
smaller).
Rename `PresentationCocycle` to `FpGroupCocycle` and offer to calculate a
faithful permutation representation for it.

REBASE: Local variables, avoid the global Gpword fct. for order issues.

TWOCOHOM: Added test

ENHANCE: Allow for different presentations for better rewriting

Added IsomorphismFpGroupForRewriting and method for alternating groups.

ENHANCE: Avoid duplicate test, build on existing permrep first.

REBASE: Examples reflect new code. Make immutable.

ENHANCE: IrreducibleModules spins cheap submodules first

Spin submodules spanned by augmentation ideal vectors for first submodul
chain and chop, to avoid irreducibility tests in large regular module.

Also flag fix for `TrivialModule`.

ENHANCE: Homomorphisms for 1-dimensional modules just is common eigenspace.

REBASE: Factor out radical part stemming from P-core

REBASE: Simplify presentation before trying permrep.

ENHANCE: CompatiblePairs also works if group is not solvable

So far this case is a naive stabilizer calculation.

REBASE: Generic compatible pairs routine

ENHANCE: Action of compatible pairs

REBASE: Better compatible pairs

REBASE: Burnside-Brauer method

REBASE: Force natural An for presentation.

REBASE: Special case of abelian reps.

TWOCOHOM: Better rewriting, store ordering for monoid pres.

REBASE: use pres.

REBASE: Preserve (so far only single) RWS.

REBASE: Simplify presentation before finding subgroup quotients

Run Tietze in LargerAbelianQuotient with different heuristics

lib/twocohom.gi

@@ -1408,8 +1408,7 @@ local r,z,ogens,n,gens,str,dim,i,j,f,rels,new,quot,g,p,lay,m,e,fp,old,sim;
   SetSize(fp,Size(r.group)*Size(r.module.field)^r.module.dimension);
 
   if Length(arg)>2 and arg[3]=true then
-    #sim:=IsomorphismSimplifiedFpGroup(fp);
-    sim:=IdentityMapping(fp);
+    sim:=IsomorphismSimplifiedFpGroup(fp);
 
     g:=r.group;
     quot:=InverseGeneralMapping(sim)*GroupHomomorphismByImages(fp,g,GeneratorsOfGroup(fp),