Implement "Simple" Views Bulk Operations (VBO)

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This is a followup to Views in core. Once Views is included, we need to start converting administrative interfaces to use it.

Drupal 8 implemented a "simple" version of VBO in core that did not include actual "bulk" operations, queuing, or batching. Instead, it implemented simple actions that set a temporary value and redirect the user to the existing pages provided by node and user module to perform operations on a group of nodes or users.

Here are two examples:

• Nodes: Convert admin/content to a View, keep a non-views fallback with no bulk operations
• Users: Replace admin/people with a View

In our case, we'll be less elaborate yet with our set of changes. Instead of rewriting the underlying actions system, we'll probably leave actions mostly as-is and simply provide a few additional actions that redirect to the node/user operation pages. Looking over the code base of VBO for D7, one enhancement that we may want to include is is the "actions_permissions" module (bundled with VBO), allowing for a more flexible access to individual access.

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I filed an initial PR for VBO at backdrop/backdrop#134. It adds the new handler for bulk operations and exposes it to comments and nodes. It also removes some unnecessary actions that never really made much sense in the first place (manually saving nodes or comments), and don't apply at all for our situations in core now that Trigger module isn't around any more.

This patch doesn't yet include any implementations (or tests) of the bulk form. Considering we'll be adding both in #149 and #150, this PR is only any initial pass.

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I merged in backdrop/backdrop#134 to unblock our actual implementation issues for VBO. Let's finish individual implementations in #149 and #150.