Acts as taggable

Creating tags for videos to be used for searching and categorizing 
This doesn't seem like the write formatting.
something like
```ruby
add_index(
  :taggings,
  [ :tag_id, :taggable_id, :taggable_type, :context,:tagger_id, :tagger_type ],
  unique: true, name: "taggings_idx"
)
```