Estonian & Latvian flavors, translations & small fixes

* The Czech flavor had an unused `gender` attribute in clean method
* Add EE (Estonian) flavor: zipcode, personal identity code and county fields
* Add LV (Latvian) flavor: postal code, personal code and municipality fields
* Change LT (Lithuanian) flavor: do proper normalization in postal code field (both "12345" and "LT-12345" now get normalized to "LT-12345")
* Latvian translations for Latvian municipalities
* Estonian translations for Latvian municipalities, Russian areas and many more texts.

If you want me to change something (squash commits or split to multiple pull requests), let me know.