Better display of the logfile in the server status window

[gleu]

We need to create columns for each differents informations in the logfile (log_line_prefix is an hint to parse the log text).

[thom]

What if the user enters values which aren't for parsing? e.g. log_line_prefix = '%p - server1 - %s'

[gleu]

We would treat this as three columns:
1. %p
2. ' - server1 -'
3. %s

The second column won't be as interesting as the two others, but it won't too in the text file.