Format page title

This change adds support to set custom page titles and adds meaningful
titles for dashboard and server main views.

    ApplicationHelper
      #page_title
        given no input
          returns a default title
          includes a set content variable title
        given a string
          returns the given value
          sets the title content variable
        given any other input
          raises an ArgumentError
Merge pull request #134 from prometheus/page-title

Format page title