Add date selector loading indicator

[danieltsoukup]

Is your feature request related to a problem? Please describe.
The date selector on the sensor page is not showing the loading status when a new date is selected, the user is unaware if anything is happening.
https://dashboard.tracket.info/locations/756264

Describe the solution you'd like
Add a loading icon or similar features on top of the current graph, or replacing it to signal the loading in the background.