Using Material standard DatePicker

[bastaware]

Test users have reported that it is difficult to figure out that they need to double tap a date to select it in the Pluto Grid date-picker. Additionally, they are annoyed by the inability to manually enter a date. As a result, I have made a change to enable the use of the standard date picker. I'm not sure if it's suitable for a pull request at this time, so I'm just posting it here for now. If anyone is interested.

master...bastaware:pluto_grid:UseStandardDatePicker