Use BigDecimal with two decimal points
 - when initializing them this way, they display two decimal points when they are printed
When setting amount on Payment..
 - if not null.. create a `BigDecimal` with amount ZERO, but set to two decimal points and add the passed in amount to it
 - if null... then just set null
Merge pull request #304 from CruGlobal/EVENT-137

EVENT-137