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: I698f6fd21c67a1e55429312a0484b6c393cad46f
diff --git a/updater/install.c b/updater/install.c
index 7b4b99b..f68bd03 100644
--- a/updater/install.c
+++ b/updater/install.c
@@ -792,11 +792,12 @@
         return NULL;
     }
 
+    char* partition = NULL;
     if (partition_value->type != VAL_STRING) {
         ErrorAbort(state, "partition argument to %s must be string", name);
         goto done;
     }
-    char* partition = partition_value->data;
+    partition = partition_value->data;
     if (strlen(partition) == 0) {
         ErrorAbort(state, "partition argument to %s can't be empty", name);
         goto done;