Add status check endpoint

HabiticaApi.cs

@@ -44,5 +44,10 @@ namespace HabitSharp
             req.AddUrlSegment("model", ModelName);
             return this.Execute<Result<Dictionary<string, string>>>(req);
         }
+
+        public bool CheckStatus() {
+            var result = this.Execute<Result<Dictionary<string, string>>>(new RestRequest("status"));
+            return result.Success && result.Data.ContainsKey("status") && result.Data["status"] == "up";
+        }
     }
 }