Re-implements the locales selection with suggestions and search.

This replaces the initial implementation of a two-step locale selection
with a more advanced version, which does suggestions, search, removes
locales that already exist in the user preferences.

Bug: 25800339
Bug: 26414919
Bug: 26278049
Bug: 26275094
Bug: 26266914
Bug: 26266743
Bug: 26266712
Bug: 26266605
Bug: 26266490
Bug: 26266021

Change-Id: I88944c86e4cae5eaa00b7ae4855887ab11989253