C++ class for device-specific code

Replace the device-specific functions with a class.  Move some of the
key handling (for log visibility toggling and rebooting) into the UI
class.  Fix up the key handling so there is less crosstalk between the
immediate keys and the queued keys (an increasing annoyance on
button-limited devices).

Change-Id: I8bdea6505da7974631bf3d9ac3ee308f8c0f76e1
10 files changed