PUB-1067: Add support for pair-wise interactions option.

Example:

h2o.interaction(factors=c(1,2,3), pairwise=F) creates cubic 1_2_3 interaction.

h2o.interaction(factors=c(1,2,3), pairwise=T) creates quadratic 1_2, 1_3 and 2_3 interactions.
Merge branch 'master' of https://github.com/0xdata/h2o
PUB-1067:  Fix merge conflicts.
PUB-1067: Fix locking
Fix bug in cbind.
PUB-1067: No longer store temporaries in KV store.
PUB-1067: Properly handle a list of factors with given key.
PUB-1067: Improve documentation, show pair-wise, higher-order and self-interaction.
Merge branch 'master' of https://github.com/0xdata/h2o