forced alignment for fast_align

Made minor changes to fast_align code to support forced alignment of new data using the parameters estimated during EM on the training set.

fast_align.cc
- changed output_parameters flag to write params to file
- added force_align flag to load written params from training, skip EM (0 iterations) and align input as the testset
- added mean_srclen_multiplier flag to set mean source length multiplier manually when force aligning input.

ttables.cc/h
- added new function DeserializeLogProbsFromText() to load params from output_parameters file

Example Usage:
(1) Training
./fast_align -i training -d -o -v -p training.params > training.align 2> training.log
(get final_tension and source length multiplier from training.log)
(2) Forced Alignment
./fast_align -i test -d -T <diagonal tension from training> -m <mean_srclen_multiplier from training> -f training.params > test.align