Show Clear Date for SingleDatePicker

[Mythra]

fixes #141

This PR adds in the ability to specify showClearDates for the SingleDatePicker which is showClearDates from DateRangePicker. The main goal here is obviously to create a button which allows the user to clear the date value inside of the SingleDatePicker.

The way I set this up should be mostly identical to DateRangePicker, really the only major thing I changes was changing the usage of the word "dates" to: "date" as it just seems to "fit better" ™️ . Needless to say the functionality of the button itself, as well as the reopen on clear feature should be completely identical. Just clearing the single date, instead of multiple dates.

[coveralls]

Coverage increased (+0.3%) to 88.333% when pulling a1350be on SecurityInsanity:single_clear_date into da20c1f on airbnb:master.

[majapw]

Looks great to me! Thank you so much.