UCT pattern prior: Raise default from 80 to 160

After 500 games with single threaded (i7 HT) -t =4000, there is 44-40+22
Elo improvement here; let's optimize more for realistic scenarios for
our users even though on big cluster, 80 may be a better default.
Twiddle several Moggy playout policy parameters based on CLOP

These are CLOP experiments with pachi-29a24, single-threaded (i7-3770),
15x15 against GNUGo level 10; patterns were not used (?).
The number after [%] is |eigenvalue|.

abstime 500s            1000s           2000s           4000s
nakade  61% 3.39        80% 3.29        53% 7.62        66% 7.92
eyefill 54% 0.52        84% 0.61        49% 0.38        32% 2.45
nlib    29% 0.02        20% 0.09        22% 0.10        27% 0.28
ko      71% 0.08        63% 0.27        60% 0.33        48% 0.57
uElo SD 35              26              22              39      (smaller is more confident)

Just for your interest, mean winrate during tuning:
komi    -35.5           -40.5           -50.5           -50.5   (to give GNUGo an advantage)
Elo     140             164             84              101

Nota bene:
- 4000s S.D. single-threaded translates just to 500s S.D. (8 minutes)
  8-threaded, which is still faster than a regular KGS blitz.
- In general, 500s and 4000s values are unfortunately of low confidence,
  this Elo spread is more than influence of most of the parameters.

Parameter analysis:
- nakade: let's go with the rough mean of 60%, which seems to hold.
- eyefill: we see a clear downward trend; let's go with 40%, more
  tuning needed.
- nlib: we see about constant 25% optimum, but the feature is not
  very interesting in general.
- ko: steady decrease, but 40% may hit closer to home in realistic
  KGS setting.

Overally, after 500 games, the performance changes as follows (komi -55):

-Elo uElo +Elo (+-1SD)
361  377  392  prior=pattern=80,playout=moggy:nakaderate=20:nlibrate=20:korate=20:eyefillrate=60
396  411  427  prior=pattern=160,playout=moggy:nakaderate=20:nlibrate=20:korate=20:eyefillrate=60
384  399  414  prior=pattern=160,playout=moggy:nakaderate=20:nlibrate=25:korate=40:eyefillrate=60
404  420  435  prior=pattern=160,playout=moggy:nakaderate=60:nlibrate=25:korate=40:eyefillrate=40

Not too conclusive, unfortuinately, but it seems we should have a slight
improvement.