Create a mass balance tester / reporting tool using the integration api

[benjaminleighton]

Using the a combination of integration api /locations and /location/overlap endpoints:

1. Use the locations endpoint Iterate over all base geometry units (at the moment, meshblocks and contracted catchments)
2. For each unit use the overlaps endpoint to find out the overlaps with this base geometry within the same spatial hierarchy.
3. Make sure that the sum of the areas / proportions of overlapping geometries up the hierarchy at each level sum to the same area as the other corresponding set in the other layers.