more comments in CentralIdempotentsOfInvolutiveAlgebra
removed obsolete code in PrincipalBlockIdempotent

which is guaranteed by CentralIdempotentsOfInvolutiveAlgebra
declared and installed BlockOfIdempotent
used BlockOfIdempotent to simplify PrincipalBlock
UnderlyingGroupAlgebra is now an attribute
declared CoefficientsRingForPolynomialAlgebra

and set it in BlockOfIdempotent
enhanced comment
and IsAlgebra( e![1001] )
BlockOfIdempotent now cashes its result

e![1234] := B;
DefiningIdealOfUnitaryGroup is now an attribute
separator
declared and installed the properties Is*OfAffineSpaces

. IsCotangentPartUnionOfAffineSpaces
. IsLowerPartExtensionOfAffineSpaces
declared and installed attributes relying on HasCoefficientsRingForPolynomialAlgebra

. DefiningIdealOfUnitaryGroup
. DefiningIdealOfSemiSimplePartOfUnitaryGroup
. DefiningIdealOfCotangentPartOfUnitaryGroup
. DefiningIdealOfRadicalPartOfUnitaryGroup
. DefiningIdealOfLowerPartOfUnitaryGroup

+ adapted the name of the caching component in corresponding operations
simplified code for PrincipalBlockIdempotent
declared and installed CentralNonPrincipalIdempotentsOfGroupAlgebra
renamed SemiSimplePart -> UpperPart
renamed CotangentPart -> MiddlePart