Add a new column with difference of values and update the total

There is a difference in the total values for construction material and basement presence for different types of main usage.

To solve this, we add an additional type i.e. unknown into basement presence. The number of buildings in this type is the difference between the totals.

i.e. current version:

main usage construction material number_buildings_cm presence of basement number_buildings_bp
office total 12000 unknwon -
office unknwon - total 10000

Adding additional type

main usage construction material presence of basement number_buildings
office total total 12000
office total unknown 2000

Also, updates the total for basement presence to the ones for construction material (here considering that the numbers coming from construction material are the correct ones.

\rfc @ds @tara

Edited by Simantini Shinde