Instead, we use XModule field default values when creating an empty
XModule. Driven by this use case, we also allow for XModules to be
created in memory without being persisted to the database at all. This
necessitates a change to the Modulestore api, replacing clone_item with
create_draft and save_xmodule.

attempt to test xmodule_modified (see fixme)
Removed obsolete else clause from before conversion
Ensure factories use datetime not struct_time for start date
Added more unit tests for settings encoder