c nnbsp - selective resp. automatic insertion of nnbsp

[BOberreither]

Some c-elements are superfluous (not actually in the witness); they represent nnbsp characters to be displayed throughout the document in the reading version only; the topogr. transcription has to show them only on printed witness pages. C-elements are to be partially removed, nnbsp-display in reading version done automatically (not based on c elements).