Improve ComDirect PDF-Importer (#5759)

- Rename addDividendeTransaction() to addDividendTransaction() to follow English naming convention
- Normalize currency values with asCurrencyCode() when storing into document context (currency and foreignCurrency keys in addFinancialReport())
- Add missing hasExDate(null) to all 127 dividend assertions in the test and add the corresponding import
- Fix three hasTaxes("EUR", 0.0) → 0.00 to use double literal for zero amounts
- Rewrite testFinanzreport13 to use Hamcrest matchers instead of assertTrue/assertEquals, remove WHAT-comments, add missing results.size() assertion, and remove the now-unused org.junit.Assert imports

Author: Nirus2000