Added support for locale on DatePicker dialog component

[aabilio]

Updated components, docs and spec.

[aabilio]

This is not a PR to address #623, just a simple way to provide strings to DatePicker to show months and days in other languages (with some predefined languages loaded).

[javivelasco]

Beautiful work! I think this is very useful and does not create any breaking changes so happy to merge! Thanks 💃 !

[sanfilippopablo]

This is great. When is this going to be on NPM?
Edit: Nevermind. I see it's on the latest release (1.1.1).

[aabilio]

I just realize that action buttons ('Cancel' and 'OK') need to be translated too. I was thinking on inserting it in locale prop too (pro: easy api for Date Picker component) but I think that inserting new properties like okButtonLabel, cancelButtonLabel, dismissButtonLabel... could make sense too (pro: standarization of action buttons). What do you think @javivelasco?

[javivelasco]

I think they should come from props as you mentioned. In fact, all internationalization in a library such as react-toolbox should be based on that. Anyway there are not a lot of components with text so it should be easy.

[sanfilippopablo]

While the props option sounds more technically correct, I think that the labels being attributes on the locale object is more useful, because the default locale with the string locale prop is simple option that covers 95% of the use cases. Besides, it would still allow customization through the object locale prop.

[javivelasco]

Yeah maybe. It also would be a cleaner api. More opinions on this would be great