Trying to reduce memory footprint of json reads
Heavy filtering to eliminate any non-desired KA translations.
add --no-kalite-trans option
add gc collect calls to remove lingering garbage from removing
nonmetadata from po files
add extra msgblock removing logic into polib.py itself
solve issue #1289: use POFile.merge for concatenating files instead of msgcat
convert prep_inputs into a generator
properly remove extra msgblock headers
Fix POEntry merging
run remove_exercise_nonmetadata only on exercises
play with po file filtering
Merge commit 'dbaaf5fa4e4b909a489008ce69c97c9c00b7486b' from Ben into 1293

Conflicts:
	kalite/i18n/management/commands/update_language_packs.py
fix some merge bugs to make update_language_packs work again
add new --low-mem option
convert use of filter into itertools.filter
convert prep_inputs back into generator
Merge pull request #1305 from aronasorman/1293

Reduce memory consumption of update_language_packs