editor/viewer dialog: newlines and whitespaces in text (FoLiA v2.5)

[proycon]

The editor dialog currently present a single-line input box, newlines are simply stripped. This is fine for editing tokenised text consisting of words as they are by definition single-line, but is an issue when editing untokenised text such as paragraphs. As we strip newlines, sentences get glued together. The editor dialog does correctly show the spacing.

1. Currently the editor dialog can not deal with text-markup (of which newlines are a special instance). Full editing of text-markup support it complex and out of scope, but we can envision at least a fix for newline situation, presenting a <textarea> rather than an <input> for structural elements above the word level.

2. The second issue is whitespace handling, the editor dialog actually shows this correctly, but the viewer dialog does not (nor does it show explicit newlines), we should base ourselves on the htmltext attribute rather than the text attribute for the viewer dialog.

This is related to proycon/foliadocserve#16 and the whitespace changes in FoLiA v2.5 in general.

[proycon]

Rather then extend to editor to support newlines, for now it simply renders newlines as spaces. This is consistent with the fact that editing text-markup is not supported and provides a fairly simple solution.