Add stats report for multisite usage

[sybrew]

A Multisite network counts as one user.

Troy Client doesn't report this yet, and Troy Server doesn't process this.

1. We want to report on how many Multisite networks use a plugin (and aggregate a total across all plugins/themes served).
2. We may want to collect information about the number of sites that are using a plugin in the multisite.
   • If a plugin is network-activated:
     1. We should report that.
     2. We should add the number of sites to the total count.