Teach ng WorkPackagesHelper to format 'currency' type

Still missing L10n support: currently EUR symbol is hard-coded.

User Story # 5225

Signed-off-by: Alex Coles <alex@alexbcoles.com>
Teach #column_data_type to handle CurrencyQueryColumn

Since this class is only available in a plugin, we need to handle
match against its class name as a String. A better long-term solution
should be found for plugins to add their own data type.

User Story # 5225

Signed-off-by: Alex Coles <alex@alexbcoles.com>
Merge pull request #1237 from opf/fix/work-package-costs-plugin-currency-type

Fix/work package costs plugin currency type