Try to add new features to cpu/mayah
Reformat plain_field.cc

Follow the other sources style.
Reformat client_connector.
Stylefix: reformat drop_decision.h
Remove workaround for duel in src/core/client/ai/ai.cc

Since we have 1 sec before starting a new game, we don't need to have
workaround in src/core/client/ai/ai.cc
Rename ai_routine to mayah_ai.
Improve cpu/mayah/learn a bit.
MayahAI: preparing for reviving learnFromPuyofu.