GUI: Add countdown & cancel to install auto-reboot

Provide a countdown from 5 sec for the automated reboot after install.
Include a cancel button to interrupt the process.

Change-Id: Ib5e1447918adfde45eba361c088800812b690890
diff --git a/gui/objects.hpp b/gui/objects.hpp
index 84a9e5e..0d96927 100644
--- a/gui/objects.hpp
+++ b/gui/objects.hpp
@@ -313,6 +313,7 @@
 	int cancelzip(std::string arg);
 	int queueclear(std::string arg);
 	int sleep(std::string arg);
+	int sleepcounter(std::string arg);
 	int appenddatetobackupname(std::string arg);
 	int generatebackupname(std::string arg);
 	int checkpartitionlist(std::string arg);