Kwcoco

Fixed
* Taking non-existing channels from a single-image delayed node returns a
concatenated node with existing and nan channels.

Changed
* Taking subchannels from a concatenated delayed node now groups discontinuous
indices from the same underlying image.
* `channel_spec`, `sensorchan_spec`, `util.lazy_frame_backends`, and
`util.delayed_ops` have all been ported to the new `delayed_image` package.

Removed
* Removed old `util_delayed_ops`

Fixed
* Fixed bug in vidshapes toydata code
* Respect masked arrays when doing delayed warp

Changed
* Handle change in kwimage demo data, doctest hashes changed
* The SQLView changed the "extra" key to "__unstructured__" and now implicitly
removes it before being passed to the user.
* The multisensor data now contains a "sensor" key in the image dictionary.
* Can now pass `kwcoco.CocoDataset.coerce` `sqlview=True` to attempt to grab an SQL view of the dataset.

Fixed
* bug in coco subset when absolute=False

Changed
* Officially deprecate `kwcoco.util.util_delayed_poc`
* Remove the 2 suffix on the official `delayed_ops` node names.
* The delayed crop method can now simulated a padded slice.
* Changed ujson integration from opt-out to opt-in. Specify `KWCOCO_USE_UJSON` to use ujson.

Changed
* kwcoco will now use ujson to read json files by default if it is available.
* Added runtime deprecation noticed to deprecated functions
* Doctests now generate images for readthedocs.

Added
* Ability to "undo warps" from delayed ops.

Changed
* Removed Jagged from `delayed_ops`
* NaNs are now optimized like other leafs.

Fixed
* Bug where delayed nan did not have the right warp signature.
* Bug in boids when speed was 0.