Add helper functions which determine if an expression is real.
Todo: One could do more sophisticated stuff with expressions of
the form "M Adj[M]" which are allways real.
Make couplings real which contain only real variables
Add special rules for Conj(x) * x which is always real.
Properly initialize the coupling result
The tests of the meta code depend on the meta code itself
Avoid decomposing Times[a,b,c] if a,b,c do not contain SARAH`sum.
This will result in simpler code, because Conj[x]*x can be simplified
to AbsSqr[x]
Simplify the multiplication of the different factors after the
expansion of the sums.  Since we now call RvalueToCFormString on
the the whole product, more AbsSqr[] fimplifications are applied.