Count up total data size to help with backup pricing #25
Description
Since we can get a host's data size from /api/public/v1.0/groups/GROUP-ID/hosts/HOST-ID/metrics/DB_DATA_SIZE_TOTAL let's make it so we can grab the data size of each entry (i.e. each replica set/cluster), and display it along with a total at the bottom. Ideally, this should be smart enough to measure and display cluster as a cluster, rather than as a series of replica sets.
This probably fits best under the metrics command.