Add firstname gender method to all Person provider

Hi,

This is a missing feature already implemented in some localized Person provider but useful to all Person Providers.

The refactoring is not completed and I need some help to separate male and female firstname.

Concerned files have this comment : 

```php
// TODO separate male and female firstname
```

Remaining localized Person classes which need male and female firstname separating : 

- [x] ~~bn_BD~~
- [x] ~~bg_BG~~
- [x] ~~cs_CZ~~
- [x] ~~da_DK~~
- [x] ~~de_AT~~
- [x] ~~de_DE~~
- [x] ~~el_GR~~
- [x] ~~en_AU~~
- [x] ~~en_CA~~
- [x] ~~en_GB~~
- [x] ~~en_PH~~
- [x] ~~en_US~~
- [x] ~~es_AR~~
- [x] ~~es_ES~~
- [x] ~~es_PE~~
- [x] ~~fi_FI~~
- [x] ~~fr_BE~~
- [x] ~~fr_CA~~
- [x] ~~fr_FR~~
- [x] ~~hu_HU~~
- [x] ~~hy_AM~~
- [x] ~~is_IS~~
- [x] ~~it_IT~~
- [x] ~~ja_JP~~
- [x] ~~nl_BE~~
- [x] ~~nl_NL~~
- [x] ~~me_ME~~
- [x] ~~pl_PL~~
- [x] ~~pt_BR~~
- [x] ~~ro_MD~~
- [x] ~~ro_RO~~
- [x] ~~ru_RU~~
- [x] ~~sk_SK~~
- [x] ~~tr_TR~~
- [x] ~~uk_UA~~

Some firstnames remain unknown
- [x] en_ZA
- [x] lv_LV
- [x] sr_Cyrl_RS
- [x] sr_Latn_RS
- [x] sr_RS
- [x] zh_CN