Update comment creation code

[adeneys]

The comment creation process currently traverses the content tree lookig for the post item by template. A better way to do this would be to look for the first non-comment and non-folder item in the ancestors. Makes this piece of code more flexible.

[adeneys]

It looks like the only reason the current code looks for the blog item during comment creation is to read settings and determine the appropriate template to use for the comment item. We should extract the settings to a provider model where settings can be read from configuration or a blog item. That would allow creating comments on non-blog items.