add ransack gem
add search form for web users#index
remove paging options
rename created_at to pretty_created_at for decorators
remove text_preview from post decorator
add search form for web posts#index
add translations for search forms
Merge branch 'feature/ransack' into develop

Conflicts:
	app/controllers/web/posts_controller.rb
	app/controllers/web/users_controller.rb
	app/views/web/posts/index.html.haml
	app/views/web/users/index.html.haml