[Sprites] add sprites for icon images
[Sprites] add sprites for branding
[Sprites] social media logos sprite usage
Merge branch 'develop' into diaspora_with_sprites

Conflicts:
	Gemfile
	Gemfile.lock
	app/assets/stylesheets/application.css.sass
	app/assets/templates/comment_tpl.jst.hbs
	app/assets/templates/stream-element_tpl.jst.hbs
	app/helpers/aspects_helper.rb
	app/helpers/contacts_helper.rb
	app/views/aspects/_aspect_listings.haml
	app/views/aspects/toggle_contact_visibility.js.erb
	app/views/contacts/_aspect_listings.haml
	app/views/layouts/_header.html.haml
	app/views/shared/_footer.html.haml
	app/views/tags/_followed_tags_listings.haml
[Sprites] update sprites after develop merge
add assets:preocompile prerequisite for cucumber specs on CI
added sprites to .gitignore
Merge pull request #4039 from marpo60/diaspora_with_sprites

Add Sprites to Diaspora!
update changelog [ci skip]