New commenting system

Daisy currently includes a very simple system to add comments to documents. There is lot of room for enhancement here.

Some ideas:

• allow to associate/attach comments with parts of the documents (e.g. individual paragraphs or headers). For a nice example, see here.
• allow threaded comments
• allow to edit comments afterwards
• translate links in comments to clickable text (e.g. "daisy:" and "http:" should be translated to links)
• or allow very simple richt-text (just pargraphs, bullets, links, bold, ... editor should load very fast)
• allow searching on comments (both searching in the content of comments, as well as identifiers for the query language to retrieve e.g. the number of comments a document has)
• allow comments by anonymous (guest) users, i.e. it should then be possible for commenters to leave name, email and url. That will require integration with spam protection services such as Akismet, or else provide some user-friendly CAPTCHA system.
• ...