Fix a bunch of messages

* Find and rename/remove duplicate string variable names
* Add missing string variables to en language file
* Fix display of some strings missing @ in front of variable name
* Fix several %s --> {1}
* Be consistent in usage of cancelled vs. canceled (both spellings
  acceptable)

Tip for finding strings missing from language files:

1) Find all messages:
egrep -hr "gui_msg.+=" > /tmp/msgs.txt

2) Regex replace to trim them down
WHAT: ^\s+gui_msg(?:[^"]+)"([a-zA-Z0-9_]+)=([^"]+).+
WITH: $1
Note that $2 can be used to retain the message

3) Find missing strings:
for i in $(cat /tmp/msgs.txt); do
    if ! grep -q $i gui/theme/common/languages/en.xml; then
        echo $i;
    fi
done

Change-Id: Ic193162e4b5468bf027472928a370be39840ea1d

gui/action.cpp

@@ -347,7 +347,7 @@ void GUIAction::simulate_progress_bar(void)
 	{
 		if (PartitionManager.stop_backup.get_value()) {
 			DataManager::SetValue("tw_cancel_backup", 1);
-			gui_msg("backup_cancel=Backup Canceled.");
+			gui_msg("backup_cancel=Backup Cancelled");
 			DataManager::SetValue("ui_progress", 0);
 			PartitionManager.stop_backup.set_value(0);
 			return;
@@ -1197,7 +1197,7 @@ int GUIAction::nandroid(std::string arg)
 		}
 		else {
 			DataManager::SetValue("tw_cancel_backup", 1);
-			gui_msg("backup_cancel=Backup Canceled.");
+			gui_msg("backup_cancel=Backup Cancelled");
 			ret = 0;
 		}
 		operation_end(ret);