Use -target_only option when fetching sequences from BLAST+ database.

BLAST+ sometimes returns more than one sequences for an accession number when
querying nr/nt database. The sequences returned are identical except their id.
This behaviour is unintuitive and causes SequenceServer to warn users that the
databases might be incorrectly formatted. Using -target_only ensures BLAST+
will return the exact match for the queried accession.

Signed-off-by: Anurag Priyam <anurag08priyam@gmail.com>
Enable -hash_index switch when creating databases.

Should make things faster.

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