MDL-31636 Add optional time formatting to get_comments()
MDL-31636 Added optional time formatting to comments ajax handler.
MDL-31636 Added strftimeformat args to output functions
MDL-31636 Added strftimeformat to javascript pagination calls.

I've never tried so hard to integrate one miserable option into an API.
Hopefully this one option helps a little.
I tried to not make it a part of the comment 'class' as its just a timestamp to the class.
This is really an output option. Thus, the strftimeformat option is passed through the entire API(php & js & nonjs).
It only has to be specified to the output() call like so:
        $output = $comments->output(true,$strftimeformat);