update KEYSPACE to specify short key names

computers don't care
use a shorter default prefix
lua implementation of get_alternative_by_client_id

and delete the unused has_converted_by_client_id
shorten key names to conform w/ updated CLIENTSPEC
test conversion
fix _get_stats
whitespace
kill unused collection models
control is a property
rename get_alternative_by_client_id
whitespace
sequential ids are stored per experiment

This will prevent memory usage from growing uncontrollably for conversion/participations keys. It also means that memory can be fully reclaimed when experiments are deleted.
cache sequential ids again
kill unused property
fix experiment version caching