Revise investment performance report

1. "amount" (last column) has been replaced by "ending balance" because

it's calculated specially for this report by
QueryTable::constructPerformanceRow,

2. "return on investment" column is being calculated also when "ending

balance" is zero, because zero ending balance doesn't invalidate ROI

3. "buys" and "sells" column take "fee amounts" into account during ROI

calculation, because fees are inseparable from investments,

4. "buys" column has minus sign and "sells" column has plus sing,

because the same notatnion is used by KMM importers.

REVIEW: 129739
Signed-off-by: Łukasz Wojniłowicz <lukasz.wojnilowicz@gmail.com>