[DatePicker] Add option to hide date display

[dhoward]

This adds an option to hide the date display above the date picker (or on the side on portrait mode). I did not add any unit tests because this is purely a visual change, but the code has been linted and docs have been added.

Thanks for the awesome library!

• PR has tests / docs demo, and is linted.
• Commit and PR titles begin with [ComponentName], and are in imperative form: "[Component] Fix leaky abstraction".
• Description explains the issue / use-case resolved, and auto-closes the related issue(s) (http://tr.im/vFqem).

[stunaz]

By doing so, you lost the ability to choose the years

[dhoward]

@stunaz yes that is true, sorry I forgot to mention that. I figured it would be ok since you already have a disableYearSelection option for users who do not need that functionality. I could add a line in the documentation something like “Hiding the Date Display will also hide year selection” to clarify that this will hide both. Does that sound ok?

[oliviertassinari]

This extra option sounds fair to me.

did not add any unit tests because this is purely a visual change

There is no reason why visual changes shouldn't be tested. I would even advocate for the opposite, they are the most tricky ones.
It's more a changing rendering logic here. I small unit test at the React level would be great.

[oliviertassinari]

I have some consideration for the naming convention and the API consistency. With boolean properties, we have two options. showX/hideX I think that we should be choosing based on the default value. That's basically what have been done at the HTML specification, e.g. disabled, readonly with the input in order to allow the shorthand.
Let's follow the same convention. with hideX as the default is going to be false.

TL;DR What about hideCalendarDate?

[mbrookes]

By doing so, you lost the ability to choose the years

#4949 would solve that.

[dhoward]

@oliviertassinari thanks for the feedback, I have renamed the prop and added unit tests for showing/hiding the date.

It looks like TravisCI is failing due to lint errors in a couple unrelated files, I see at least one of them is already being addressed in #6182, not sure about the other one but I can add a fix on this PR if that would be helpful.

[oliviertassinari]

Thanks.