split fisheye changeset email template to a daily/batch one and an immediate one

Fisheye changeset email templates are monolithic in that both batch and immediate changeset notifications are using the same template, making the templates hard to edit, as well as very large with embedded logic - e.g., in the subject, the size of the changeset is used to determine whether to display the commit message or not.

Should split them up into two templates, one for handling batch, one for handling immediate, and factor out the common parts into a #include file (like common-body).