Revert "Renamed the sqlite database from kb.db into kb.sqlite"
Revert "Renamed the sqlite database from kb.db into kb.sqlite"

The change was not motivated in the commit message, and the database
was still named 'kb.db' in many places. Better to revert this commit for
now.

This reverts commit 47f7a08d15179633b23e020fc67a4b8d936208d4.

severin-lemaignan/minimalkb