Fix various UX bugs.

* In the drag & drop list align numbers with the + in
  the "+ Add a language" button
* Keep the "+ Add a language" button under the list
* Shadow cell while drag & drop
* Updated various strings for dialog titles and messages

Bug: 26557242
Bug: 26710677
Bug: 26712004
Bug: 27070104
Change-Id: I10d26eac9581c955328e667d7309b5f0ac649110