Working version without feature engineering, 0.094 LB
again
WIP for Interactions.
Merge branch 'master' into arno-features

Conflicts:
	R/examples/Kaggle/TradeShift.R
Merge branch 'master' into arno-features
Add mean imputation of training data, based on group-by on response.
Merge branch 'master' into arno-features
WIP
Merge branch 'master' into arno-features
PUB-1067: Initial version, makes pair-wise quadratic features.
PUB-1067: Working for higher-order features.
TODO: add self-interaction (order 0) to limit the number of factors
PUB-1067: Add support for 0-th order (self-) interaction, to limit the number of categoricals of a feature.
Added support for min. occurrence threshold, to only keep factors that appear often enough.
Cosmetics.
PUB-1067: Add timing info.
PUB-1067: Minor cleanup, speedup.
PUB-1067: Use binary search for faster Enum mapping.
 PUB-1067: Add H2O parameter -data_max_factor_levels <integer> to specify the max number of categorical factors per column.
 Defaults to 65000.
Merge branch 'master' into arno-features
PUB-1067: Add h2o.interaction() function to R.
PUB-1067: Refactor such that the resulting Frame has only the interaction Vec.