sophia: reorganize LSN life-cycle

Make it consistent about LSN numbers during
different work phases.

Introduce db.commit_lsn.
Make it possible to set LSN number to any object.

LSN synchonization cases:
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a. index recover
b. log recover
c. two-phase recover case (ctl: db.two_phase_recover)
d. run-time LSN forge (ctl: db.commit_lsn)