Better explanation when filtered by host

[bestchai]

Currently, the filtering by host is indicated visually, but there is no textual description of what the resulting graph represents. It would be helpful to expose text to the user that explains what filtering by host means. Perhaps this text can be enabled/disabled (e.g., visible in just a tutorial/help mode).

[Issue created by bestchai: 2014-07-15] [Last updated on bitbucket: 2014-08-26]