Detect previous but still executing request and cancel

[programcsharp]

If refreshing for whatever reason, and there is a previous request, cancel it before executing the next one.

Also ensure that the loading spinner goes away in all cases, even rapid paging/filtering an errors.

[ithielnor]

The loading spinner is not part of griddly.

[programcsharp]

The request canceling part is, though. I noted the spinner here to make sure it's tested through.