Fixed login link redirection in comments
Fixed preview param name
API Removed ajax comment submission

The JS logic didn't account for edge cases like scrolling
to the inserted comment, or attaching the comment in the right sorting logic,
on the right pagination page. It also doesn't show any "loading" indication,
so is bad usability for the majority of users. A standard form submission
does the same job better in this case. Note that this doesn't affect
the ability to moderate/delete comments via ajax.

Replaced 'use_ajax_commenting' with 'include_js',
since its important for behaviour other than comment submission itself,
e.g. showing previews (doesn't work without JS)