FIX-#431: Moving and adding sampling to backend calculations

[westernguy2]

Overview

This is a branch that builds off of the work done in #432. This moves the sampling to after the Filter and also adds sampling for metadata computation.

Changes

Changes the execute function to move sampling after the Filtering is done, and so the sampling is done on each of the data visualizations. It also edits compute_data to sample the data before computing the metadata. All metadata is the metadata associated with the sample, not the full dataset.

Example Output

N/A