Do more to help BI tool visualizations (aggregate mode)

[mikix]

Outside of a Cumulus context (i.e. in aggregate output mode), the experience could be a lot better for creating a BI-tool-based visualization. This is a ticket to unify discussion of that (and probably actual work will be documented in other tickets and PRs). This is also related to the more data-focused #33.

Some thoughts on improvements:

• Unify tables in some cases into one unioned summary view (i.e. in aggregate mode, c_resource_count might appreciate unioning all the various resource tables into one summary table - so that BI visualizers don't have to do that work themselves).
• There might also be other cases where we want to see a variant of a table in aggregate mode that wouldn't make sense in cube mode. (see Add resource_cnt column to c_system_use tables #31 and Add resource_cnt column to c_us_core_v4_count #32 for example)
• Tracking changes in data metric results over time is another interesting delta between Cumulus and local/BI mode. See Consider tracking trends of data metrics over time #34.