Add support for editing alternative names for people

[mhl]

Previously there was no support for adding, deleting or editing alternative names for people in YNR, although this is supported by the Popolo data model.

This commit adds basic support for editing alternative names for people; the page for managing a person's other names is linked to from the person edit page under their full name.

Fixes #749

Things still to do (although this is usable without them):

• [x] Restrict editing to logged in users
• [x] Fix the position of the triangle on the source confirmation pointing up to the "Delete" button
• [ ] Make the display of these changes in the version history more readable
• [x] Add some tests to exercise these new views

  Link to the alternative names page

The alternative names page

The add new name form

[wfdd]

Some of the text hasn't been marked up for translation (line 30 in the person form, etc.).

[mhl]

@wfdd I hope I've marked up the remaining strings in 2bb8812 but do let me know if I've still missed some.

[wfdd]

Just the one; thanks.

[struan]

This looks good to me.