Allow content blocks to be visible or not based on hierarchy role.

The new Information Channel implemented in the December Software Upgrade is a good idea and it would be great if Administrators could use a similar box to post notices to specific users as well. At the moment, Administrators have to resort to the dashboards to relay messages but most users prefer to be redirected to "My dashboard" when they log on. Also, only the main School Dashboard and "My dashboard" can be set up as default log-in landing pages, which makes things even more difficult.