Filter events

Filter events and group them to make it easier to view events

## Before
![membership admin 2](https://cloud.githubusercontent.com/assets/2305016/4884746/bf3c2450-636e-11e4-85ed-68858f28a6e9.png)

## After
![membership admin 1](https://cloud.githubusercontent.com/assets/2305016/4884751/c75ecd54-636e-11e4-964c-c4cda91a8b0a.png)