Improve string on accounts page

Setup (the noun) should be set up (the verb).

https://bugzilla.gnome.org/show_bug.cgi?id=726487
Improve a string on the enterprise login page

A network administrator is singular and can type "his or her" password,
not "their" password. Let's say just say "the password" to avoid any
awkward phrasing.

https://bugzilla.gnome.org/show_bug.cgi?id=726487