* feat: Implement paste button
* chore: improve docs and add tests for python API
* fix: drive-by fix to use a better API for comparing XML
* feat: track which XBlock something was copied from
* feat: add tests
* feat: enable import linter so content_staging's public API is respected
* fix: error seen when trying to paste drag-and-drop-v2 blocks
* fix: use strip_text=True consistently for XML comparisons
* refactor: rename get_user_clipboard_status to get_user_clipboard
* feat: Better error reporting when pasting in Studio
* chore: convert new test suite to pytest assertions
* refactor: push READY status check into the API per review suggestion
* fix: use strip_text=True consistently for XML comparisons
* fix: store "copied_from_block" as a string to avoid Reference field issues
* fix: minor lint error
* refactor: move data types to data.py per OEP-49
This commit implements STUD-1490, allowing creation of components
on the container page. It also enables the delete and duplicate
buttons now that new content can be created that would benefit.
Note that it also creates shared functionality for adding components,
and refactors the unit page to use it too.
