Update MongoDB container tag to `3.0`.
Doc change to reflect bdb-config.bdb-user parameter usage.
Fix typo in configuration.md.
Add BIGCHAINDB_DATABASE_SSL parameter to bigchaindb-dep.yaml for
Kubernetes deployments.
Refer the the `bdb-user` parameter from ConfigMap in
bigchaindb-dep.yaml.
Consolidate all BigchainDB parameter values under the
`bdb-config` ConfigMap.
Remove `bdb-user` from secrets.yaml.