Moveable Custom Time Range Filter

__Proposal:__
A UX change to the Custom Time Range selector to allow it to be dragged.

__Current behavior:__
When selecting Custom Time Range, the PopUp Date Selector often blocks the data. Making it hard to pick an exact time if the user is trying to narrow in on a specific time range.

__Desired behavior:__
The ability to drag/move the Custom Time Range PopUp box within the Data Explorer.

__Alternatives considered:__
The ability to click a timestamp in the rawdata view and have it populate the Start time.

__Use case:__
During data exploration, I find myself following these steps:
-executing a generic query with a broad time range
-wanting to easily narrow in on a specific time range, but having to write the timestamps down, so that I can specify them in the date picker.
The following picture demonstrates how I can't view the hidden data covered by the date picker.

Start in the InfluxDB Data Explorer's Custom Time Range selector and reproduce the popup obscuring the data shown in the issue. Determine how the selector can be dragged within the explorer, then verify that users can move it to reveal data while choosing an exact range.

Written by the indexing model from the issue text.