Add LabeledFrame table to the GUI

[talmo]

Problem: Currently, LabeledFrame instances are not represented graphically in the GUI other than in the suggestions. This makes it hard to search for specific types of frames that meet particular criteria.

Desired columns:

• Video (index? filename? full path?)
• Background frame flag (#640)
• Number of total instances
• Number of predicted instances
• Number of user labeled instances
• Number of "consumed" predicted instances (ones that have a Instance associated with them)
• Number of low scoring predicted instances (using a fixed threshold?)
• Average scores for predicted instances
• Last interacted (or interacted recency?) like labels.context.state["last_interacted_frame"] which is used in GoLastInteractedFrame

More broadly: this table widget and table data model should be flexible enough to incorporate other types of search criteria, possibly including dynamically defined ones where the user sets a manual threshold. Examples:

• minimum distance between head and abdomen across instances
• minimum time since track spawn
• average velocity

Some might be very performance intensive, so we should curate a subset that are more useful and leave room for future expansion that is more flexible.

Related issues: #640, #641