Use same placeholder in JS as non-js

The placeholder for nojs  (action=reply)
is a snippet of the post being
replied to for context.  JS should use the same.

Additionally the no-js placeholder was reading something like:

    Reply to "<p data-parsoid="{...}">actual content</p>"

strip the tags from it to get just the text content.

Additionally switch from ->text() to ->plain() to prevent
the parsing of magic words inside content as part of the
i18n message.

Change-Id: I6308c428c2d707a684527854fa5d08675949d996