Handle less thans in map summary

[kathymd]

• [x] Exclude results that are marked as less thans from being plotted in the map
• [x] Keep less than results included in the map download csv
• [x] Update the User's Guide to explain that they're in the map download but not plotted

This will be consistent with how the graph plotting/download and will ensure that less thans aren't included in the map pop-up summaries.