addressing the occasional issue in which the marker would get placed even when no attributed features were under the location, also leaving the feature attribution overlay open.  feature attribution overlay and marker now behave as intended, both only showing on mouse clicks on attributable features
removing Source and/or Notes from Learn pages when no content is present
lining up the data catalog links
adjusting descriptive and other context for various data layers...will need to load from data manager initial_data fixture...