Add a datetime filter

[dgkf]

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.