load data asynchronously and incrementally

## Use Case

Data loading currently blocks the whole application and is not easy to cancel. This is most obvious during a time series render when in between times, loading is blocking everything.

## Solution

This is pending any unexpected technical limitations related to multithreading with various file format libraries.
1. Put data loading on a thread.
2. Make thread cancellable by looping and polling for interruption
3. Allow incremental re-rendering during async loading.
4. Would it benefit from using multiple threads?