Move some number printing methods to System-NumberPrinting

[jecisc]

I found out that we had a package System-NumberPrinting but some methods from Kernel are calling methods from this package. Here is an iteration to move some of them to this package

[Ducasse]

I found a bit strange that printOn: does not belong to the package of the class in particular for numbers but this is ok too.

[jecisc]

Closing this PR since it's old and buggy. I'll often newer PRs