Add support for rendering video-level attributes

[brimoor]

eta.core.video.VideoLabels now has video-level attributes, which are the same as frame-level attributes but are set once and apply to all frames of the video. We need to add support for rendering these attributes via Player51.

My proposal is that video-level attributes are rendered in the same box as the existing frame attributes. Always on top of the list, say.

This proposal aligns with how video-level attributes are rendered by ETA: https://github.com/voxel51/eta/blob/develop/eta/core/annotations.py

See the example JSON on the right-hand side of the docs below to see a minimal example of a VideoLabels with video-level, frame-level, and object-level attributes:

https://voxel51.com/docs/api/#types-videolabels