Add footer-row to simple_footer.html

Since phpBB 3.2.3, the overall_footer.html template file was revised to add links of Terms and Conditions.

In addition, p tags were added, with the new class (footer-row) : these tags have created vertical "margins" (due to the property line-height for "footer-row" class, defined in theme/common.css) between different elements such as the copyright and the translation info (if you don't use the default British English) or the debug output.

These changes were not added in the simple_footer.html template file. Therefore, there is no vertical "margin" between the copyright and the translation info or between one of them and the debug output.

Thus, there is a graphical inconsistency across the board (if the current page uses overall_footer.html file, the footer text is airy ; if it uses simple_footer.html instead, the line-height of the footer lines is much shorter).