Created enum MessageStatus in KeychainIntentServiceHandler and enum IOType

in KeychainIntentService and replaced int constants with them. Fixed some
typos.

OpenKeychain/src/main/java/org/sufficientlysecure/keychain/util/ExportHelper.java

@@ -124,7 +124,7 @@ public class ExportHelper {
                 // handle messages by standard KeychainIntentServiceHandler first
                 super.handleMessage(message);
 
-                if (message.arg1 == KeychainIntentServiceHandler.MESSAGE_OKAY) {
+                if (message.arg1 == MessageStatus.OKAY.ordinal()) {
                     // get returned data bundle
                     Bundle data = message.getData();