ImportedPose table

[samuelbray32]

Is your feature request related to a problem? Please describe.

• Many groups have pre-existing DLC pose estimations
• Similar to spikesorting, we should have a system to import pose estimation data from the raw nwbfile prior to the PositionOutput merge table

Describe the solution you'd like

• A new table ImportedPose
  • Points to pose and skeleton data objects in the raw nwb file
  • Use the ndx-pose extension to store and read PoseEsitmation and Skeleton objects in the nwb file
• Feeds into PositionOutput so entries can be used for further behavior analysis (e.g. Moseq)
• Has function fetch_pose_dataframe returning result consistent with the DLCV1 pipeline