[Tagging] Optimize Tag Loading for Several Specific Objects

[bradenmacdonald]

For the Course Outline Page, we may need an optimized way to load the count of tags for each unit among "all units in the course" instead of loading them one unit at a time. (see the tag count shown for each unit in #118 )

We also need a more optimized way for the "get object tags" API to return the ancestry/lineage of each returned tag. Currently it just returns the actual tags.

Likewise, for the Unit Page in Studio and the Library Page, we may need an optimized way to load the tags for "all components seen on this page" instead of loading them component by component. (Actually it seems the current version of the UI doesn't indicate which components have tags?)