Change default time settings from -t =80000 to -t 15

Change default time settings from -t =80000 to -t 15

This loses a semi-nice property that Pachi will by default have
the same strength on any computer, but on the other hand it will
make Pachi adjust its strength based on the computer without playing
needlessly fast or taking way too long time per move. This should be
more user friendly. Suggested by Jean-Loup.