Do not show principal cost centers in the columns of step-down cost allocation report

[jniles]

Here is the current step-down cost allocation report, we currently have every cost center listed in the columns. This doesn't make sense. We should only have the cost centers that are being allocated in the columns.

Here is the current report with fake data from the Vanga dataset:

Notice how many columns we have! But we only have 3 auxiliary cost centers that are allocating their costs. We should only have three columns.

Here is an example for Essentials of Healthcare Ch. 13:

See how there are four cost centers, but only two columns, since only two of the four cost centers are auxiliary cost centers. This is what we should be doing.

[jniles]

I'll tackle this one.