Override default datepicker locale

[maxokorokov]

It looks like it's not possible to override the datepicker locale on a per-datepicker / component basis, but only at the app level:

• we @Inject(LOCALE_ID) private _locale in the NgbDatepickerI18nDefault
• we have only one instance of the i18n service in the NgbDatepickerModule : {provide: NgbDatepickerI18n, useClass: NgbDatepickerI18nDefault}

Note that NgbDatepickerI18nDefault is private.

So we probably should move {provide: NgbDatepickerI18n, useClass: NgbDatepickerI18nDefault} to the datepicker component instead of the module, so you could override locale anywhere.

However, in this case we should inject NGB_DATEPICKER_LOCALE_ID that will use LOCALE_ID by default not to interfere with the rest of the application.