Revert "Merge pull request #4039 from marpo60/diaspora_with_sprites"

This reverts commit 8f6ae75423fbd1482a58e257e89a55f66fa19838, reversing
changes made to 5a26d0b639f7338b2ebf41aa1154da97f099edac.

Conflicts:
	Gemfile
	Gemfile.lock
	app/assets/stylesheets/application.css.sass
	app/assets/templates/header_tpl.jst.hbs
	app/views/shared/_right_sections.html.haml