Edit metadata caching

The functionality provided by this project has been merged with both the Drupal 7 backport of Edit module (#2178567: Backport: Use client-side cache tags & caching to eliminate 1 HTTP requests/page for in-place editing metadata, introduce drupalSettings.user.permissionsHash) and Edit module in Drupal 8 core (#2005644: Use client-side cache tags & caching to eliminate 1 HTTP requests/page for in-place editing metadata, introduce drupalSettings.user.permissionsHash).

Therefore this project is now obsolete.

Overrides Edit's metadata to be cached in sessionStorage. Only works for sites that have simple permissions.

By "simple permissions", we mean that as long as a user still has the same set of permissions, the same action will always be allowed. I.e. only the permissions determine whether in-place editing of a specific field is allowed, not context like time, location, IP address, workflow state, language and so on.

A concrete example where this module would cause problems: if a journalist creates a story, then edits the title in-place, the metadata for in-place editing will have been cached in the journalist's browser. But if the journalist then changes the workflow state to "needs review" so that the editor-in-chief might approve it, then the journalist is no longer allowed to edit it. However, the cached in-place editing metadata in the journalist's browser will not be cleared, since the journalist still has the same set of permissions; it's not the roles/permissions system that determines whether the journalist may edit the story, it's the workflow state.

Ideally, we'd have this kind of metadata in Drupal core, but we currently don't have this yet, hence we cannot be smart about caching this yet.