Feature: Added options to toggle the visibility of mini_profiler

Two options have been added:
1. It is now possible to load the page with mini_profiler hidden
2. It is now possible to toggle the visibility with a shortcut

To handle the toggle shortcut, jquery.hotkey.js was added to the
project.
Merge pull request #112 from elhu/feature-toggle-display

Feature: Added options to toggle the visibility of mini_profiler