Block: Announce structural course changes at course overview

There are different announcements at course overview like new forum post and new assignments. It would be nice to have added/updated/deleted mods announced as well.

This behavior would be similar to the recent activity block - but only on startpage. I have changed the core code and would like to contribute/help on this topic. As well as it may be nesseccary to alter the mods as well (for proper output).

I have code, which works on 2.6 so far. But since it is mostly just additions to the original code, I think it's applyable on 2.7 as well. It's working, but in order to make it nice and shiny we need to discuss in which direction it should go.