Includes admin base_helper to attachments_helper and adds specs.

The BaseHelper is now included in the AttachmentsHelper because the used _t method is defined in the BaseHelper.
Merge pull request #415 from robinboening/admin_attachments_helper_specs

Includes admin base_helper to attachments_helper and adds specs.
Removes two (soon to be) deprecated elements helper methods.
Moves a element url helper into url_helpers module.
Adds specs for admin/pictures_controller.
Fix bug in crop picture view.
Merge branch 'refs/heads/2.7-stable'