Basic models for historical accounts
First failing feature
Rework people administration

People now have historical accounts as well as translations, so it
makes sense to give them a show page with tabbed navigation to manage
all the things.
Add admin for historical accounts

Just basic CRUD for now.
Eager load translations
Remove unused template
RoleAppointment is aware of historical accounts
Scope for role appointments between dates
Custom url helper for historical accounts

The helper allows us to link to a historical account, defaulting to
the first role for the given account. We can pass in a role override,
which allows us to link to the account scoped to a different role,
specifically for when the account applies to multiple roles
Link to historical account frontent from admin
Front-end for historic appointments
Allow role appointments to have older dates...

... so we can add the historical accounts dating back to 1700s.
Do not repeat people who have had multiple terms
Make year ranges dynamic based on appointments
Don't list duplicate roles

We only want to see each role the person was appointed to appear
once in the select list
fixup feature
Optimise admin/people#index

Now we have an admin/people#show, we no longer need the links to
manage translations and delete people on the index page, instead
leaving those controls on the show page. This reduces the number of
associations to be loaded and speeds things up considerably.
Make url helper more consistent

We talk about historic appointments when dealing the with front-end,
i.e. the combination of a person and a role in a historic context.
The fact that that person may have a historical account in that role
should not be of concern to the url helper.
Add missing table heading to fix markup
Rename people list to historic people list

So it can be reused all over the historic people section.