deprecate Activity

[brynnz22]

Regarding issue: microbiomedata#1552

• Remove the Activity class from the schema
• Move Activity slots over to WorkflowExecutionActivity class
• change activity_set slot for the Database class to workflow_execution_set
• Change references like domain and range values from Activity to WorkflowExecutionActivity

[brynnz22]

will not require a migration

[brynnz22]

I guess this will actually need a migration because we have a collection called activity_set in Mongo and this renames it to workflow_execution_set. Though it is an empty collection in Mongo, so it seems like a bit of a silly migration. @turbomam @eecavanna. Does this actullay need a migration?

[brynnz22]

I can add this bit to the migrator that already exists for renaming collections.