Add personal settings for stream activities

Already has some new settings and email included, but these options are hidden
from the UI until the activities themselves are implemented.

Fix #1705 

Screenshot of the current list:
![2014-03-19_13 37 18](https://f.cloud.github.com/assets/213943/2459934/72e19bb8-af63-11e3-8fc8-e7c0f0ada3b8.png)

**Note:** There are more settings included aswell as emails, but they will not be visible in the UI until I implemented them correctly, therefor the settings page is rather short at the moment

@karlitschek @jancborchardt