Added new public parseNSErrorAsJsonString method

* Designed to be used by other SDKs as a standard way to parse errors from postNotification.

Author: jkasten2

iOS_SDK/OneSignal/OneSignal.h

@@ -265,6 +265,7 @@ typedef NS_ENUM(NSUInteger, ONE_S_LOG_LEVEL) {
 + (void)postNotification:(NSDictionary*)jsonData;
 + (void)postNotification:(NSDictionary*)jsonData onSuccess:(OSResultSuccessBlock)successBlock onFailure:(OSFailureBlock)failureBlock;
 + (void)postNotificationWithJsonString:(NSString*)jsonData onSuccess:(OSResultSuccessBlock)successBlock onFailure:(OSFailureBlock)failureBlock;
++ (NSString*)parseNSErrorAsJsonString:(NSError*)error;
 
 // - Request and track user's location
 + (void)promptLocation;

iOS_SDK/OneSignal/OneSignal.m

@@ -473,7 +473,7 @@ + (void)postNotification:(NSDictionary*)jsonData {
 }
 
 + (void)postNotification:(NSDictionary*)jsonData onSuccess:(OSResultSuccessBlock)successBlock onFailure:(OSFailureBlock)failureBlock {
-    NSMutableURLRequest* request = [httpClient requestWithMethod:@"POST" path:@"notifications"];
+    NSMutableURLRequest* request = [httpClient requestWithMethod:@"GET" path:@"notifications"];
 
     NSMutableDictionary* dataDic = [[NSMutableDictionary alloc] initWithDictionary:jsonData];
     dataDic[@"app_id"] = app_id;
@@ -506,11 +506,30 @@ + (void)postNotificationWithJsonString:(NSString*)jsonString onSuccess:(OSResult
     if (jsonError == nil && jsonData != nil)
         [self postNotification:jsonData onSuccess:successBlock onFailure:failureBlock];
     else {
-        onesignal_Log(ONE_S_LL_WARN,[NSString stringWithFormat: @"postNotification JSON Parse Error: %@", jsonError]);
-        onesignal_Log(ONE_S_LL_WARN,[NSString stringWithFormat: @"postNotification JSON Parse Error, JSON: %@", jsonString]);
+        onesignal_Log(ONE_S_LL_WARN, [NSString stringWithFormat: @"postNotification JSON Parse Error: %@", jsonError]);
+        onesignal_Log(ONE_S_LL_WARN, [NSString stringWithFormat: @"postNotification JSON Parse Error, JSON: %@", jsonString]);
     }
 }
 
++ (NSString*)parseNSErrorAsJsonString:(NSError*)error {
+    NSString* jsonResponse;
+    
+    if (error.userInfo && error.userInfo[@"returned"]) {
+        @try {
+            NSData* jsonData = [NSJSONSerialization dataWithJSONObject:error.userInfo[@"returned"] options:0 error:nil];
+            jsonResponse = [[NSString alloc] initWithData:jsonData encoding:NSUTF8StringEncoding];
+        } @catch(NSException* e) {
+            onesignal_Log(ONE_S_LL_ERROR, [NSString stringWithFormat:@"%@", e]);
+            onesignal_Log(ONE_S_LL_ERROR, [NSString stringWithFormat:@"%@",  [NSThread callStackSymbols]]);
+            jsonResponse = @"{\"error\": \"Unkown error parsing error response.\"}";
+        }
+    }
+    else
+        jsonResponse = @"{\"error\": \"HTTP no response error\"}";
+    
+    return jsonResponse;
+}
+
 /* Option:0, 1 or 2 */
 + (void)setNotificationDisplayOptions:(NSNumber*)option {