feat(toolbar): add button to hide/show toolbar

menu.jade:
* Add toggle button to toolbar
* Add container to hide the rest of toolbar without hiding the toggle
button.

menu.styl:
* Add toggle button styles
* Update toolbar styles to account for toggle button

header.styl:
* Update rules for adding and removing padding from .header-wrap when
toolbar is toggled.
Merge pull request #3402 from benmanley/toolbar-toggle

feat(toolbar): add button to hide/show toolbar