kbx: A minor update of the fingerprint table.

* kbx/backend-sqlite.c (table_definitions) <fingerprint>: Add columnt
'flags'.

Updates-commit: 0cc7759ed5a3890b4e28563a6b5e97f3aa551530

We are anyway updating this table and thus we can also reserve a
column for future use. No need for a a new database version after
less than 24 hours and no release for the previous change.