invoice: payment: refactor rounding logic

Respect the correct amount of decimal places for each currency.

Note that upgrading an existing system with that patch can yield to
non-deterministic results as the pro-ration code has been changed to
support 9 decimal places: this will lead to different pro-ration amounts
due to rounding.

Signed-off-by: Pierre-Alexandre Meyer <pierre@mouraf.org>
Merge branch 'master' into new-amount-decimals-handling-rfc
util: add missing copyright header

Signed-off-by: Pierre-Alexandre Meyer <pierre@mouraf.org>
Fix typo for currency precision config file
Merge remote-tracking branch 'origin/master' into new-amount-decimals-handling-rfc

Signed-off-by: Pierre-Alexandre Meyer <pierre@mouraf.org>

Conflicts:
	beatrix/src/test/java/com/ning/billing/beatrix/integration/overdue/TestOverdueIntegration.java
Merge remote-tracking branch 'origin/new-amount-decimals-handling-rfc' into new-amount-decimals-handling-rfc
Merge remote-tracking branch 'origin/invoice2' into new-amount-decimals-handling-rfc

Signed-off-by: Pierre-Alexandre Meyer <pierre@mouraf.org>

Conflicts:
	beatrix/src/test/java/com/ning/billing/beatrix/integration/TestBundleTransfer.java
	beatrix/src/test/java/com/ning/billing/beatrix/integration/TestIntegrationInvoiceWithRepairLogic.java
	beatrix/src/test/java/com/ning/billing/beatrix/integration/overdue/TestOverdueIntegration.java
	invoice/src/main/java/com/ning/billing/invoice/generator/DefaultInvoiceGenerator.java
	invoice/src/test/java/com/ning/billing/invoice/dao/TestInvoiceDao.java
	invoice/src/test/java/com/ning/billing/invoice/generator/TestDefaultInvoiceGeneratorRepairUnit.java
Merge remote-tracking branch 'origin/master' into new-amount-decimals-handling-rfc
Merge remote-tracking branch 'origin/invoice2' into new-amount-decimals-handling-rfc

Signed-off-by: Pierre-Alexandre Meyer <pierre@mouraf.org>

Conflicts:
	beatrix/src/test/java/com/ning/billing/beatrix/integration/TestSubscription.java
	invoice/src/test/java/com/ning/billing/invoice/TestInvoiceHelper.java
	invoice/src/test/java/com/ning/billing/invoice/tests/inAdvance/annual/TestProRation.java
	invoice/src/test/java/com/ning/billing/invoice/tests/inAdvance/quarterly/TestProRation.java
Merge remote-tracking branch 'origin/master' into new-amount-decimals-handling-rfc