Fix edited_by_human? and all the tests

Fix remainder of specs to supply a user when versioning is on

Make the features pass by supplying a stub user for mappings
Make the trait :as_stub_user unnecessary

* In favour of stubbing a default user when one is not set and PaperTrail is enabled
Reword the test for PaperTrail requirements

* Avoid the if/unless combination
Reset PaperTrail config for features as well as specs
Set PaperTrail config in mapping spec more concisely
Add comment on PaperTrail setup in bulk adder spec
Move as_a_user into Transition::History

...from Whitehall mappings CSV import
Use as_a_user in 2 tests for precision

This is clearer than setting the user and then making changes to
mappings in setup.
Remove a redundant mapping factory as_user use

We only need to use this now when we care about the user; if we don't
care who it is then the factory will use a stub user for the whodunnit.
Move logic to ensure config into Transition::History

It isn't a concern of the Mapping model to know when or how PaperTrail's
config should be set. It just needs to be able to be confident that the
config is ok before saving a mapping.
Rename method more concisely with !

The ! seems appropriate since it will raise an exception if the user
config is not set when it should be. This method is now in the History
module so its name doesn't need to refer to papertrail.