Divide the `UPDATE` statement to calculate the total built up area in one tile into a one `SELECT` and multiple `UDPATE` statements

The deaggregation can come to a halt because the UPDATE statement that calculates the total built up area of tiles takes long and can create a big lock on the tile table. However, the SELECT statement inside the UPDATE statement is the one that takes some time, not the UPDATE itself. It is better to have many small update statements, based on one big SELECT that has been done beforehand.

\fyi @ds @gislars