recovery: Factor out wear_ui.{cpp,h} into bootable/recovery.

Every watch has a (mostly identical) copy of the wear_ui. Factor them
out into a single copy for easier maintenance. Device-specific settings
should be defined in recovery_ui.cpp that inherits WearRecoveryUI class.

Bug: 22451422
Change-Id: Id07efca37d1b1d330e6327506c7b73ccf6ae9241