New 'site' assignment plugin

Problem/Motivation

A common component of a features set is a "site" feature, which collects configuration needed for the site but not specific to focused use cases. Configuration assigned to such a feature might include sitewide menus and blocks, shortcut sets, and text formats.

Proposed resolution

• Create a new 'site' assignment plugin.
• Add a configuration form to select the configuration types that should be assigned to it.
• Give it a relatively high default weight, allowing other assignment plugins to run first.
• By default, assign the following:
  • block (Block)
  • block_content_type (Custom block type)
  • contact_form (Contact form)
  • menu (Menu)
  • search_page (Search page)
  • shortcut_set (Shortcut set)
  • editor (Text editor)
  • filter_format (Text format)
  • tour (Tour)
  • view (View)

Remaining tasks