recovery: Allow bypassing signature verification on non-release builds

For non-release (userdebug, eng) builds, when signature verification
fails, ask the user whether they wish to install anyway.

[aleasto]
Rewritten to minimize the diff footprint for maintainability

Change-Id: I950ad455e6f698cabe348f0482eb64287cc88a08
diff --git a/recovery_ui/device.cpp b/recovery_ui/device.cpp
index 0e96b1e..4408c9f 100644
--- a/recovery_ui/device.cpp
+++ b/recovery_ui/device.cpp
@@ -74,6 +74,7 @@
 }
 
 Device::Device(RecoveryUI* ui) : ui_(ui) {
+  ui->SetDevice(this);
   PopulateMenuItems();
 }