Consolidate sources' date formatters

[dkcm]

These sources maintain their own date formatters, which can be consolidated:

1. FinancialContent - MM/dd/yy and yyyyMMdd
2. GlobalView - M/d/yyyy
3. GoogleFinance - dd+MMM+yyyy, d-MMM-yy, yyyyMMdd
4. Investopedia - MM/dd/yyyy
5. MoneyControl - yyyy-MM-dd
6. Morningstar - MM/dd/yyyy
7. MotleyFool - yyyy-MM-dd
8. OnVista - dd.MM.yyyy
9. Quandl - yyyy-MM-dd
10. WallStreetJournal - MM/dd/yyyy, MM/dd/yy, yyyyMMdd

[dkcm]

Converter and Interval also have date formatters (yyyyMMdd).