Add toString overrides for some ServerCode classes

Author: echipachenko

src/com/backendless/servercode/ExecutionResult.java

@@ -55,4 +55,13 @@ public void setException( ExceptionWrapper exception )
   {
     this.exception = exception;
   }
+
+  @Override
+  public String toString()
+  {
+    return "ExecutionResult{" +
+            "exception=" + exception +
+            ", result=" + result +
+            '}';
+  }
 }

src/com/backendless/servercode/RunnerContext.java

@@ -91,4 +91,18 @@ public void setPrematureResult( Object prematureResult )
   {
     this.prematureResult = prematureResult;
   }
+
+  @Override
+  public String toString()
+  {
+    return "RunnerContext{" +
+            "appId='" + appId + '\'' +
+            ", userId='" + userId + '\'' +
+            ", userToken='" + userToken + '\'' +
+            ", userRole=" + userRole +
+            ", deviceType=" + deviceType +
+            ", missingProperties=" + missingProperties +
+            ", prematureResult=" + prematureResult +
+            '}';
+  }
 }

src/com/backendless/servercode/logging/Logger.java

@@ -135,4 +135,13 @@ static String dumpStack( Throwable t )
     pw.close();
     return sw.toString();
   }
+
+  @Override
+  public String toString()
+  {
+    return "Logger{" +
+            "async=" + async +
+            ", clazz=" + clazz +
+            '}';
+  }
 }