fix(filters): handle the current locale correctly

The NumberFormat uses the locale which is set when the formatter is
initialized. This means a NumberFormat should be cached for each locale.

Closes #865
feat(http): Allow overriding of recording URL.

Moving hardcoded recorder URL to config class and can be overridden by installing extended PlaybackHttpBackendConfig class in applications.

Closes #872
fix(DateFilter): cache DateFormat correctly

- cache named date formats (such as 'medium', 'short' and so on...)
- cache DateFormat for each locales