Don't make preferences window resizable

There's no scrollable content, so no reason to make the dialog
resizable.

https://bugzilla.gnome.org/show_bug.cgi?id=741514
Don't make author details resizable

There's no scrollable content, so no reason to make the dialog
resizable.

https://bugzilla.gnome.org/show_bug.cgi?id=741514