Activity notifications try 2

CC @manuq

(Pretty much the same as last, but with what @tchx84 added)
FYI: It says it can auto merge, so out of date bits shouldn't be an issue

`toolkit pr` https://github.com/sugarlabs/sugar-toolkit-gtk3/pull/114

>I added the ability for activities to do the notification dance. The ui is just the systems notification ui but merged with the activity palette. I added a activity.notify function in the toolkit and will push that soon... Here is a picture (all else is shared with other notifications):
> 
> ![image](https://f.cloud.github.com/assets/6022042/2363780/0accd6d0-a655-11e3-9389-d96636eb9d6d.png)