Add a datetime filter

We lack a datetime filter! For within `shinyDataFilter` the goal is to support all base data types. Most likely, `shiny::dateRangeInput` would be the best candidate for the UI.

It is also worth considering how this input should be visualized. Given that this is a continuous field, but entered as start and end time in `dateRangeInput`, there's no clear way to visualize the distribution of data against this input UI. I'm entirely open to suggestions around how it might be best to visualize this range.