add coverage tracks for CNVs (percent callable, deletion burden, and duplication burden)

[elissa-alarmani]

Currently, this PR correctly implements the percent callable track for the CNV dataset and queries all 3 tracks (percent callable, deletion burden, and duplication burden track).

TODO:

• Decide on the best ways to visualize the 3 tracks
• Front-end visualization of deletion burden track (create components such as ./GenePage/CopyNumberVariantsGeneDeletionBurdenTrack.tsx and ./RegionPage/CopyNumberVariantsRegionDeletionBurdenTrack.tsx
• Front-end visualization of deletion burden track (create components such as ./GenePage/CopyNumberVariantsGeneDuplicationBurdenTrack.tsx and ./RegionPage/CopyNumberVariantsRegionDuplicationBurdenTrack.tsx
• Testing of the deletion and duplication burden tracks.

[elissa-alarmani]

Useful testing region and genes for the percent callable track:
Region: 1-50375975-50768099
Genes: OSBPL9 and CLSPN

[rileyhgrant]

Closing as stale