Add "delay before" and "delay after" mode to surrounding search

### Problem description

For me it is frequent case, when I want look at messages after some other message, or before it.
Currently it is not really handy, because my surrounding search may contain many pages. So I need to open surrounding search, export it in csv and then inspect it in some text editor (and often order it before).

It will be great to add new menu items, like "1 second after" and "1 second before"
### Environment
- Graylog Version: 2.0.3