ReplaceTextTask

@Wikia/platform-team 
Migrating over ReplaceTextJob. *Not* migrating over the "replace text in articles" functionality, since that doesn't work for us because we store a reference to the article text in the "text" table, rather than the article text itself, which this extension assumes.

Piggybacking: support BaseTask::batch($tasks) to queue multiple BaseTask's in one go