Add new apache date format for file listings in http sources

According to Apache source code ( http://svn.apache.org/repos/asf/httpd/httpd/trunk/modules/generators/mod_autoindex.c ), the date format changed long time ago from "10-jan-2014" to "2014-01-10" .
```
apr_strftime(time_str, &rv, sizeof(time_str),
                                 "%Y-%m-%d %H:%M  ",
                                 &ts);
```
Before the date format was: "%d-%b-%Y %H:%M  "

I didn't find the specific svn revision where this changed, but Apache 2.2 already had this date format for a long time.

This patch adds a new apache date file format so it's compatible with old and new versions of mod_autoindex. 
I added CDateTime::MonthNumToMonthString in order to not touch the rest of the code.
No need for the braces here (if you have them, please each one on separate lines as per the rest of the file).