Rename (new) success_ml to DW::Controller->render_success

We put back the original success_ml, which matches error_ml in form

But we now also have a new function DW::Controller->render_success which
has a signature which acts a lot like DW::Controller->render_template

The first argument is the page name (scope) where the success message is
defined -- it will probably match the page name in your
DW::Controller->render_template

This page should define a .success.title and a .success.message

The second argument (optional) is a hashref of any variables in the
.success.message

The third argument (optional) is a list of links in the form of:

  { text_ml => ..., url => ...}
Merge pull request #800 from afuna/render_success

Rename (new) success_ml to DW::Controller->render_success