Add GroundTruthContainer for training data
Add GroundTruthContainer for training data

A container class keeping all training data in a prepared format in
memory. Moderately sized ground truths (~2000 lines) fit comfortably
into memory speeding up training considerably, although it may be
necessary to add a from-disk switch for larger ones.

mittagessen/kraken,mittagessen/kraken,QuLogic/ocropy,mittagessen/kraken,mittagessen/kraken,QuLogic/ocropy