EXO: Refactored keyboard configuration interface

Move keyboard configuration out of server.cc
This CL only moves code around.

Bug: 896710
Test: Built on ChromeOS
Change-Id: Ia40aa6614ff1d386bdb3241c0fee9499d73d18a7
Reviewed-on: https://chromium-review.googlesource.com/c/1320655
Reviewed-by: Daniel Nicoara <dnicoara@chromium.org>
Reviewed-by: Daniele Castagna <dcastagna@chromium.org>
Commit-Queue: Shawn Gallea <sagallea@google.com>
Cr-Commit-Position: refs/heads/master@{#608500}
4 files changed