Issue #724686 by dafeder, bojanz - Add a 'force single' option, making VBO show radios instead of checkboxes

Core actions integration: Add back support for the 'behavior' key, save explicitly all entities that need to be saved (as specified through behavior).

Remove redundant code from actions_permissions (since actions_list() in D7 returns the custom actions as well).

Use operation type 'entity' instead of 'system' for actions that work on all entity types. That matches the Rules terminology.

Pass the full entities when aggregating results for an action, not just the ids (since everything is already loaded anyway). Tweak the 'pass ids to url' and 'execute script' actions a bit.

Move VBO's validate / submit logic to custom callbacks, implementing hook_views_form_validate / hook_views_form_submit will get expensive once more modules start implementing views forms.

Update the default views (the default content view was throwing a notice), point the user to them in the README.

Since views_form has been merged into views, remove the views_form dependency and make VBO compatible with the newest changes.