Paginate the Wikis and Extensions steps from Distribution Wizard

Currently if you have many wikis and you upgrade using Distribution Wizard you'll get a long Wikis step because it lists all the available wikis. Also, if you have many extensions installed on these wikis you'll get a long Extensions step. Neither of these steps scales. Ideally we should have a live table with wikis and extensions but for 5.x the quick fix is to paginate those steps.