Add the R conversion character to layouts

[sergio-bobillier]

The r character in the pattern strings outputs the number of milliseconds elapsed between the creation of the Layout and the time of the log entry. This is okay but sometimes it is easier to get an idea of the elapsed time between two log entries when the elapsed times are presented in seconds, not in milliseconds. Therefore I added the R character which output basically the same value but formats it as a floating point number with 4 decimal places.