Add possibility disable "Requests per sec" chart on server view

We have too mush subdomains and this page freeze browser. Would be nice disable this chart or reconfigure it - do not display line per hostname (use only single line)

![fireshot screen capture 008 - metalloprokat_prod intaro pinboard - pinba_server_ metalloprokat_prod_all_overview](https://cloud.githubusercontent.com/assets/191082/7810271/37811ee0-03a9-11e5-978d-f0b8f33c8bda.png)
