sprites
Use a ::before pseudo-element for icons in shelf.

The ::before pseudo-element gives us more control over the exact output
dimensions and positioning of the icon.
Remove unused and duplicate widget icons.
html.admin.scss was missing widgy_common.
Use widgy_common.scss in django.fusionbox.scss
Merge pull request #230 from fusionbox/fix_scss_errors

Fix scss errors
need to ignore demo/static too
Merge pull request #227 from fusionbox/sprites4

Sprites for widget icons
Give restoring pages a slug

Recent Mezzanine's page context processor requires something non-null
Only show interesting approve/unapprove buttons

For old commits, approving or unapproving them won't actually do
anything. Once we get to the first approved commits, we can stop showing
the approve/unapprove buttons.