declared and installed PrincipalTableBlock
declared and installed the table blocks attr NrIBr

+ compute it in the constructor TableBlocks if the 2-block is special
+ print it in the View method if the 2-block is special
suppress the computation of B!.DefectClassesOrder for the moment

as it triggers ConwayPolynomial
(observed while computing table 2-blocks of groups of order 214)
declared and installed IsMultiSpecial