Fix/window race around

[Animesh404]

What kind of change does this PR introduce?

a WIP PR for bugfix #816
Summary

• removed data from WindowEvent model and created a new model A11yEvent which points to the relevant WindowEvent
• updated crud by adding insert_a11y_event
• made changes in record where we use queue to map which WindowEvent is waiting for its corresponding A11yEvent
• added a11y_event in dashboard.

Checklist

• My code follows the style guidelines of OpenAdapt
• I have performed a self-review of my code
• If applicable, I have added tests to prove my fix is functional/effective
• I have linted my code locally prior to submission
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (e.g. README.md, requirements.txt)
• New and existing unit tests pass locally with my changes

Other information
This is still a WIP PR.