Pull out common CSS styling out of BackgroundUploadController.

Move the common CSS into users.css.scss.
Add custom profileBg HTML class that will hold background image.
Split background image and page text.

In order to make the background image opaque without affecting all
child elements, we have to split them into respective HTML siblings,
and modify the parent element slightly. The process is described in
the following blog: http://www.impressivewebs.com/css-opacity-that-doesnt-affect-child-elements/
Minor code cleanup (per Atom's standards)
Change width of content HTML element to avoid overflow.
Merge branch 'master' into make-background-image-opaque-22

Conflicts:
	app/assets/stylesheets/users.css.scss
	public/templates/profileForm.html
Add black background overlay on top of image.
Add black overlay image to user's profile show page.
Add parent div to users#show to display darkened original image.

* Remove blackOverlay div from previous commit.
Merge pull request #25 from vitaliyg/make-background-image-opaque-22

Make background image opaque 22