GUI: Terminal command: minor improvements

* Use mono font for terminal command input
* Recognize 'exit' command (go to main page)

Change-Id: I5f383cd8d19959a49d2ae0b18f839b86e4145693
diff --git a/gui/action.cpp b/gui/action.cpp
index f9de4e9..16a550b 100644
--- a/gui/action.cpp
+++ b/gui/action.cpp
@@ -1321,6 +1321,10 @@
 	if (simulate) {
 		simulate_progress_bar();
 		operation_end(op_status);
+	} else if (arg == "exit") {
+		LOGINFO("Exiting terminal\n");
+		operation_end(op_status);
+		page("main");
 	} else {
 		command = "cd \"" + cmdpath + "\" && " + arg + " 2>&1";;
 		LOGINFO("Actual command is: '%s'\n", command.c_str());