Add datepicker simple form input

[tvdeyen]

What is this pull request for?

Alchemy has a nice datepicker build on top of flatpickr.
Setting it up is a bit tedious. We have several form helpers,
but not a simple form input.

Now we have

Checklist

• I have followed Pull Request guidelines
• I have added a detailed description into each commit message
• I have added tests to cover this change

[robinboening]

Looks great! I don't have any change requests.

Only a tiny nit picky comment about the specs: I personally don't like the use of subject so much and prefer repeating the code line in the example (I find myself jumping back and forth in the file, not being able to focus on where I am reading the code). I am not asking to change it.

[tvdeyen]

Looks great! I don't have any change requests.

Only a tiny nit picky comment about the specs: I personally don't like the use of subject so much and prefer repeating the code line in the example (I find myself jumping back and forth in the file, not being able to focus on where I am reading the code). I am not asking to change it.

Fair enough. This is a general discussion about test style. I think both is fine. Whatever it takes to write specs at all 😆