Add wagtailsites views, urls and templates

Conflicts:
	wagtail/wagtailadmin/static/wagtailadmin/scss/core.scss
Add site delete view
More granular site perms, including hiding the Add/Delete buttons when not permitted
Add wagtailsites tests

Conflicts:
	runtests.py
Add page chooser panel for site form root page field
Switch to site icon and use td.title for hostname column
import hooks from wagtailcore, not wagtailadmin
add wagtailsites to INSTALLED_APPS in project template
Move Sites to the settings menu (and use decorator syntax for hooks)
styling updates to make html valid and better spacing of fields
remove unused and corrupted site_form.html
add missing styles to highlight redirects / editor's picks menu items
Rename 'Editor's picks' to 'Promoted search results' in settings menu - fixes #646