Add option to hide columns with only zeroes in multi-period balance reports

[erikryb]

It would be nice to save space by not showing columns (or rows with --transpose) that only have zero values in them, for multiperiod balance reports.

[simonmichael]

Often I have to add -E to show zero columns.. what's an example where zero columns are shown by default ?

(--transpose is currently imaginary, IIRC)

[erikryb]

It seems that by default only zero columns at the beginning or end of the report period are hidden, I think I want an option to also hide zero columns in between non-zero columns.

[simonmichael]

Ah, got it.