refactor ui functions into a class

Move all the functions in ui.c to be members of a ScreenRecoveryUI
class, which is a subclass of an abstract RecoveryUI class.  Recovery
then creates a global singleton instance of this class and then invoke
the methods to drive the UI.  We use this to allow substitution of a
different RecoveryUI implementation for devices with radically
different form factors (eg, that don't have a screen).

Change-Id: I76bdd34eca506149f4cc07685df6a4890473f3d9
diff --git a/ b/
index 2c81be6..527aa1b 100644
--- a/
+++ b/
@@ -8,7 +8,7 @@
     bootloader.cpp \
     install.cpp \
     roots.cpp \
-    ui.cpp \
+    screen_ui.cpp \
 LOCAL_MODULE := recovery