changed the link in header logo, so it always hits the debugtoolbar

This is a small change I wanted to suggest.

I often do long interactive debugging sessions with some ajax requests, with the debugger in a separate tab.

Hitting "reload" or clicking the logo will not reload after a restart/reload -- because the debugger's url is "/_debug_toolbar/{{ID}}" and {{ID}} no longer exists.  

The simple solution is to jut have the logo link to the `/_debug_toolbar/` url itself and force a full load.

nice catch.  I'll fix to use the `root_path` variable.