optimize Trog::SQLite - don't slurp/apply the schema update every startup

[teodesian]

Should check a version in a DB table, and update it whenever we change the schema file. This will be re-entrant, so we won't do the updates more than once, supposing I do a LOCK whenever deciding to update.

Should set the currently applied version number as a value I can readlink(), as that's faster than fread()