frecon: add support for multiple input devices

Also, report user activity to power_manager via dbus, so it wouldn't blank
the screen. Also enumerate input devices and handle hotplug/unplug events
using udev.

BUG=chromium:406039
TEST=emerge, deploy and run frecon, connect and disconnect USB keyboard
Change-Id: Ia536a066439fa79decb9c2aa3f2ff64e2d6447bd
Signed-off-by: Dominik Behr <dbehr@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/213216
Reviewed-by: Stéphane Marchesin <marcheu@chromium.org>
5 files changed