Add TWRP app install via TWRP recovery

Note: I will have to add a build flag for excluding the app later for
watches and maybe Android TV. I will also have to add support in the
tablet and watch layouts later. I will merge this for the initial roll out
to select devices and finish up later.

Change-Id: Ia4ce5522fae542afa1539b10c0691315392a19ab
diff --git a/gui/objects.hpp b/gui/objects.hpp
index 8d4484a..2a95022 100644
--- a/gui/objects.hpp
+++ b/gui/objects.hpp
@@ -320,6 +320,7 @@
 	int getpartitiondetails(std::string arg);
 	int screenshot(std::string arg);
 	int setbrightness(std::string arg);
+	int checkforapp(std::string arg);
 
 	// (originally) threaded actions
 	int fileexists(std::string arg);
@@ -358,6 +359,7 @@
 	int setlanguage(std::string arg);
 	int twcmd(std::string arg);
 	int setbootslot(std::string arg);
+	int installapp(std::string arg);
 
 	int simulate;
 };