Make Entity properties ```protected``` as in docs

Entity properties are marked as ```protected``` to correctly reflect the
documentation.

See also owncloud/documentation@644f2eedac8e912c3019366b29ecdfbd9a15c5d9

tests/lib/appframework/db/EntityTest.php

@@ -37,10 +37,10 @@ namespace OCP\AppFramework\Db;
  * @method void setPreName(string $preName)
  */
 class TestEntity extends Entity {
-	public $name;
-	public $email;
-	public $testId;
-	public $preName;
+	protected $name;
+	protected $email;
+	protected $testId;
+	protected $preName;
 
 	public function __construct($name=null){
 		$this->addType('testId', 'integer');		
@@ -220,4 +220,4 @@ class EntityTest extends \PHPUnit_Framework_TestCase {
 	}
 
 
-}
+}

tests/lib/appframework/db/mappertest.php

@@ -36,8 +36,8 @@ use Test\AppFramework\Db\MapperTestUtility;
  * @method void setPreName(string $preName)
  */
 class Example extends Entity {
-	public $preName;
-	public $email;
+	protected $preName;
+	protected $email;
 };