Add requests page

We already have ability to view requests in CLI, but we don't utilize the information on web client. This PR adds displaying a list of last requests for a repository:

![](http://drogus-s3itch.s3.amazonaws.com/Travis_CI_-_Free_Hosted_Continuous_Integration_Platform_for_the_Open_Source_Community-20140508-133725.png)

I don't have a single request page, but I think that I could use @roidrage's work on build header there.