Render nil as 0 in number formats

[ripienaar]

Given the report:

body: |
  @<<<<<<<<<<<<<  | @<<<<<  | @,############ | @,###### | @,####### | @,########## / @,##########
  row.config.name, row.cluster.leader, row.state.messages, row.state.num_subjects, row.state.consumer_count, row.cluster.replicas.0.lag, row.cluster.replicas.1.lag

The result has gaps, 0 would be better:

Name            | Cluster | Messages       | Subjects | Consumers | Peer Lag
----------------|---------|----------------|----------|-----------|----------------------------
NYC             | n3-lon  | 0              | 33       | 0         |              /

[ripienaar]

I'll keep this one open, we need to detect from the format what a likely data type for the null data is and then render an appropriate value like 0