Provide value stacks for columns

[ty-]

Currently this is hacked in based on the most common values returned from the ADL LRS but the viewer should support all cases.

Example of Actor Name column being populated in order of priority: actor.agent.name -> actor.agent.mbox -> actor.account.name

Similarly, object has: object.definition.name['en-US'] -> object.name -> object.id

These stacks need more fall-backs and verbs should be supported.