Convert to per-table factorizers.

### Overview

This pull request changes Sky to have one factor database per table. This should give us better performance since we are partitioning into so many mini tables.


## Changes

The main changes are:

1. Remove `tablespace` from `Factorizer` since each factorizer only works on a single table.

2. Added a `map[string]*Factorizer` that looks up factorizers for the DB.

3. Remove property name from the factorizer key and have one LMDB DBI per property. This is essentially one DB inside the LMDB environment file per property.

/cc: @snormore @mkobetic @boourns