* 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
- Moving xmodule folder to root as we're dissolving sub-projects of common folder in edx-platform
- More info: https://openedx.atlassian.net/browse/BOM-2579
- -e common/lib/xmodule has been removed from the requirements as xmodule has itself become the part of edx-platform and not being installed through requirements
- The test files common/lib/xmodule/test_files/ have been removed as they are not being used anymore
