Add email bundling function to Echo notification

* This patch needs intensive testing on Redis delayed job queue
* This patch is -2 mainly for redis/phpredis are not ready on test/test2/mediawiki

To test this locally, you need to:
* set up Redis and phpredis locally
* add the following to localSettings.php
    $wgJobTypeConf['MWEchoNotificationEmailBundleJob'] = array(
        'class'       => 'JobQueueRedis',
        'redisServer' => '127.0.0.1',
        'redisConfig' => array( 'connectTimeout' => 1 ),
        'claimTTL'    => 3600,
        'checkDelay'  => true
    );
* set $wgMainCacheType to CACHE_DB or memcache
* set $wgEchoBundleEmailInterval to smaller number for testing purpose, 0 to disable email bundling

Change-Id: I9313e7f6ed3e13478cec294b5b8408fe8e941faf