text: Title: function to explore object detection datasets
  Body: Assuming object detection data in the same format as required by methods in:
  https://github.com/cleanlab/cleanlab/tree/master/cleanlab/object_detection 
  
  Add functionality to explore basic properties about this data. For instance to compute:
  
  1.  The number of annotated objects in each image, the number of predicted objects in each image. Users can sort by these to reveal interesting insights about certain images. Eg. number of images with 0 annotations may be particularly revealing.
  
  2.  The sizes of every annotated bounding box. Users could look at boxplot/histogram and outliers here to reveal interesting insights about certain annotations. In particular, looking at the size-distribution of boxes labeled as each particular class.
  
  3.  The distribution of classes associated with each annotated bounding box. Users could look for rare classes to better understand their dataset.
   
   Plus other useful things to explore!