Improve BLAST result stats.

* Stats are now shown at the end of report, instead of once per query.
* Show individual database size and created / updated at date.
* Don't show Lambda, Kappa, Entropy, and effective search space.

API changes that follow,
* Moved Report#stats to Query#stats. Stats are the same for all queries. Dunno
  why BLAST+ XML calls it Iteration_stat and nests it under Iteration.
* Get more info from blastdbcmd when scanning databases directory for BLAST+
  databases to provide information about queried databases in the report.

Signed-off-by: Anurag Priyam <anurag08priyam@gmail.com>