Delete executions

Add ability to delete executions, bulk delete executions, and via API.

* [x] individual execution deletion
* [x] bulk delete from activity page
* [x] bulk delete from activity subviews
* [x] job delete: option to delete executions
* [x] logging
* [x] API updates: single/bulk delete
* [x] authorization: project-level access "delete_execution"
* [x] docs (authorization, ui, feature)