Hunt of DVTKIT: Move -_indentCharacterRange into XVimTextStoring

And implement all the forwarders all the way down.
Begin to remove some things from the NSTextStorage category.

Hide some -is* from the NSTextStorage category, move isLastLine as
isIndexOnLastLine on XVimBuffer.
Fix b_v_D

btw it's not 100% correct because gv doesn't quite do the right thing yet.