Drastically speed up binary file -> SQLite database generation

Using prepared queries and committing a transaction for each 100
trixels processed.

After this change, on my laptop (Intel Core i5 dual core @ 2.5 GHz, 8
GB of RAM), the db generation took about 45 minutes for USNO NOMAD 100
million stars, and the resulting SQLite DB size is 14 GB (i.e. 10x
bloat factor)